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Large Caliber Ammunition - Types of Warhead

One basic classification of types of warheads or projectiles differentiates between shells that are hollow pieces of metal containing a filler charge of some sort, and shot, which are solid pieces of metal. For convenience of discussion, large caliber ammunition may be be classified into five major groups: blast (including air and underwater burst), fragmentation, shaped charge, pyrotechnics, and cluster. The basic function of any weapon is to deliver a destructive force on an enemy target. High explosive warheads cause damage by concussion (blast effects) or by penetration of high-energy fragments. In general, there are three types of high explosive warheads that employ the latter method to accelerate metal fragments generally including (1) directed energy warheads, (2) fragmentation warheads, and (3) continuous-rod warheads (CRW). Shaped Charge Warheads refers to Shaped Charge Warheads and Explosively Formed (a.k.a. forged) Penetrators (EFPs) that are directed in that the high explosive energy is focused on a liner, which is typically made of metal. These warheads consist of a hollow liner of thin metal material backed on the convex side by explosive. Upon detonation, a detonation wave sweeps forward and hydrodynamically collapses the liner (in the case of a shaped charge) or deforms the liner (in the case of EFPs) along its axis of symmetry forming a directed jet or EFP which penetrates a localized area on a target of interest. The Shaped Charge effects concept can be used in multiples, where metal liners/projectiles are distributed, around the circumference of a high explosive charge. In this case, the detonation does not collapse a liner along its linear axis of symmetry, rather, the detonation wave hits the liners perpendicularly (almost symmetrically to the axis of the liners). High explosive fragmentation warheads constitute one of the most widely used warhead approaches in all types of ammunition. Fragmentation warheads are intended to defeat virtually all types of targets, excluding overburden targets underground and underwater, and heavily armored targets. In fragmentation warheads, the detonation of the secondary high explosive core generates a large amount of heat and gaseous products. High explosives have an extremely high rate of reaction and the presence of a detonation (shock) wave that moves faster than the speed of sound in the explosive material. Upon detonation, the metal warhead casing almost instantaneously catastrophically fails and bursts, producing a blast of rapidly expanding hot gases and casing fragments. The rapidly expanding gasses will compress the surrounding air and create a shock wave which propagates outwards at near the speed of sound in air (.about.340 m/s). The energy of the fragments dissipate more slowly than the energy of a shock wave and, thus, fragments tend to be lethal to a greater range than the blast effects for hard targets. As a function of design, fragments from a fragmenting warhead have various distribution patterns and lethality characteristics. The fragment distribution pattern is a function of the amount and nature of the explosive material (i.e. how energetic the explosion is), the mass of the fragmenting material, the fragmentation size, and the configuration (geometry, initiation scheme) of the warhead. For example, the detonation of a bomb projects the fragments in an approximate cylindrical pattern and a hand-grenade projects fragments in an approximate spherical pattern. Uncontrolled fragmentation patterns, such as those used in general-purpose bombs, occur by the natural break up of the outer casing occurring from the detonation of the surrounding explosive charge. This event forms fragments of random size and lethality. Manipulating the fragment formation process can more predictably control fragmentation patterns and fragment uniformity. Controlled fragment formation can be accomplished in several ways including: designing pre-scored failure regions (grid patterns) on the outer/inner casing or outer surface of the explosive; sandwiching an intermediate mesh material between the outer casing and the explosive core; and, arranging preformed fragments around the main charge explosive such as spheres or cubes. By controlling the fragment formation process, the relative size and, therefore, the optimized bulk fragment distribution pattern over an area is constrained to maximize the defeat probability/lethality against an anticipated target set of known thickness, obliquity, and material properties. Continuous-Rod Warhead (CRW) CRW technology incorporates two overlapping layers of ductile rods that are oriented around the circumference running parallel along the length of an explosive core. The rods are alternately connected together, end-to-end, by a weld (in a zigzag/accordion pleat fashion). Upon detonation, the continuous-rod payload rapidly expands radially outward, bending or "unfolding" the welded ends to form a ring of interconnected rods. A ring of interconnected rods is produced about the axis of the weapon. The ring expands from a highly compressed zigzag pattern to an expanded, almost flat, zigzag pattern using an expansion mechanism similar to a half-plane pantograph. During this expansion, the explosive energy is focused in a single plane such that when the rods strike a target, damage is produced by a cutting action giving it the nickname "flying buzzsaw". The metal density of a normal fragmentation warhead attenuates inversely with the square of the distance (1/R.sup.2). However, because it is non-isotropic, the metal density of a continuous-rod payload attenuates inversely as the distance from the point of detonation (1/R). To ensure that the rods stay connected at detonation, the maximum initial rod velocity is limited to the range of 1050 to 1150 meters per second. The initial fragment velocities of fragmentation warheads are in the range of 1800 to 2100 meters per second. Thus, in comparison, CRWs cannot produce as much destructive energy potential as fragmentation warheads. However, the distribution pattern is highly focused, and the rods are interconnected, to increase the relative mass interacting with a target in a highly localized area. Only one invention uses discrete rods in a fragmentation type of warhead and it closely mimics the physical architecture of the CRW (layers of rods that are oriented around the circumference and run parallel and along the length of an explosive core), but without physical interconnections being established between adjacent rods. U.S. Pat. No. 4,216,720 entitled Rod-fragment controlled-motion warhead (RFCMW) discloses destructive fragments used in a warhead that are in the form of discrete tapered rods that are substantially the same length as the cylindrical warhead itself and are placed vertically around and parallel to the axis of the warhead. The warhead system is designed to dynamically rotate the rods to form the expansion and kill radius/mechanism. U.S. Pat. No. 4,216,720 points to some deficiencies of the RFCMW concept as follows: the pattern of these rod-type fragments has been of such a discontinuous nature to results in a high likelihood of missing targets; and, the rods tend to spread in the axial direction, rather than being driven radially. Another major shortfall of the RFCMW concept is that a high explosive detonation event is used to form the geometric orientation of the rods through a dynamically controlled rotation of each discrete rod to provide the expansion mechanism. The propelling motion is empirically derived for each configuration and optimized to a 90 degree rotation for each discrete rod. If the collective interrelated system of discrete rods under or over rotates, the effective continuous coverage (end-to-end) radius is reduced. Additionally, the propellering motion of each rod within the RFCMW must have the same angular velocity (and acceleration rate) to ensure the discrete rods do not rotate into each other. The propellering motion of the discrete taper rods requires a perfectly balance rod after that rod has experience some degree of deformation following the explosive detonation of the explosive core. The detonation of the explosive charge will most likely cause spalling and material deformation of the tapered rods, which will randomly change their aerodynamic characteristics while unpredictably shifting the center-of-balance and, thus, introducing random discontinuities in the propellering motion of each discrete rod. If a single rod does not perform as designed or if one discrete rod prematurely encounters an obstacle (such as topography, a tree, etc.) before reaching the target, its rotation will be significantly altered and cause a domino effect whereby the interrelated discrete rods tumble into each other and consume the effective warhead energy. A further major shortfall in the RFCMW is the aerodynamic stability of this concept whereby the end effect must be achieved by a highly controlled formation pattern that is achieved by dynamic, balanced rotation that is highly intolerant of drift, asymmetries, and induce asymmetries such as spalling and material deformation following the warhead detonation. Time sequencing of six degrees-of-freedom motion must be achieved to propel the discrete rods radially outward, while they are simultaneously and dynamically rotating about their respective precise center axes. This requires that each discrete rod rotates at the same angular rate while experiencing a uniform velocity ratio (uniform velocity to mass ratio) during and after an explosive event across the entire length of the discrete rod which has an unusually high aspect ratio (the claimed length-to-diameter ratio is 28:1) so that all portions are subjected to both the same an outward and angular velocity to arrive at an end-to-end disposition. Other shortfalls of the RFCMW concept are as follows: the tapered rods will reduce the penetration capability at the thinned portion of the rods and therefore reduce the damage level to the intended target; and, it is doubtful that the warhead is relatively inexpensive as claimed--the warhead would be relatively expensive due to the understanding that the RFCMW requires relatively high control of rod material properties, highly toleranced machined metal parts, manufactured parts, and fabricated assemblies, and a potentially complex explosive initiation system to ensure effective results (also true for a CRW). Therefore, it is desired to provide a radially expanding kill effect similar to the CRW by using geometrically prearranged segmented circular rods placed horizontally (perpendicular to the warhead axis) around a cylindrical warhead to produce a geometrically coupled, helical spirally ring of interrelated and adjacent segmented circular rods upon detonation of the explosive core, to increase the effective mass on the target within a localized region, to create multiple impact sites within a projected height, to create lethality at and somewhat beyond the full expansion diameter of the warhead, and to create unique target defeat mechanisms compared to that of the CRW or that of all known prearranged fragmentation warheads. The Segmented Rod Warhead (SRW) is a high explosive warhead designed to radially project mechanically and geometrically prearranged fragments, in the form of multiple layers of discrete and helically wound circular segmented rods, in a prescribed, highly controlled, parallel path and radial distribution, such that at full expansion, the adjacent, individual rods align themselves end-to-end in a helical, stair-step fashion to form a continuous spiral to defeat a target, rather than pepper a target with a distribution of fragments. The expansion mechanism is radial, meaning the height of the warhead cylinder dictates the cylindrical height of the kill region. The radius at full expansion is mathematically derived from the diameter of the packaged warhead and the arc length of the discrete circular rod segments. The SRW focuses the available warhead energy on a localized area of a target in a non-isotropic fashion. This cumulative and synergistic effect greatly weakens a target by the concentration and interaction of mechanically arranged adjacent rod segments within the same localized failure region as compared to a wide spread distribution of fragments over a target of interest.

Blast

A blast warhead is one that is designed to achieve target damage primarily from blast effect. When a high explosive detonates, it is converted almost instantly into a gas at very high pressure and temperature. Under the pressure of the gases thus generated, the weapon case expands and breaks into fragments. The air surrounding the casing is compressed and a shock (blast) wave is transmitted into it. Typical initial values for a high-explosive weapon are 200 kilobars of pressure (1 bar = 1 atmosphere) and 5,000 degrees celsius.

The energetic materials used by Department of Defense munitions produce an exothermic reaction defined either as a deflagration or a detonation. A deflagration is an exothermic reaction that propagates from the burning gases to the unreacted material by conduction, convection, and radiation. In this process, the combustion zone progresses through the material at a rate that is less than the velocity of sound in the unreacted material.

In contrast, a detonation is an exothermic reaction that is characterized by the presence of a shock wave in the material that establishes and maintains the reaction. A distinctive difference is that the reaction zone propagates at a rate greater than sound velocity in the unreacted material. Every material capable of detonating has a characteristic velocity that is under fixed conditions of composition, temperature, and density.

The violent release of energy from a detonation in a gaseous medium gives a sudden pressure increase in that medium. The pressure disturbance, termed the blast wave, is characterized by an almost instantaneous rise from the ambient pressure to a peak incident pressure (Pso). This pressure increase, or shock front, travels radially from the burst point with a diminishing velocity that always is in excess of the sonic velocity of the medium. Gas molecules making up the front move at lower velocities. This latter particle velocity is associated with a "dynamic pressure," or the pressure formed by the winds produced by the shock front.

As the shock front expands into increasingly larger volumes of the medium, the peak incident pressure at the front decreases and the duration of the pressure increases. If the shock wave impinges on a rigid surface oriented at an angle to the direction of propagation of the wave, a reflected pressure is instantly developed on the surface and the pressure is raised to a value that exceeds the incident pressure. The reflected pressure is a function of the pressure in the incident wave and the angle formed between the rigid surface and the plane of the shock front.

When an explosion occurs within a structure, the peak pressure associated with the initial shock front will be extremely high and, in turn, will be amplified by reflections within the structure. In addition, the accumulation of gases from the explosion will exert additional pressures and increase the load duration within the structure. The combined effects of both pressures eventually may destroy the structure if it is not strengthened sufficiently or adequate venting for the gas and the shock pressure is not provided, or both. For structures that have one or more strengthened walls, venting for relief of excessive gas or shock pressures, or both, may be provided by means of openings in or frangible construction of the remaining walls or roof, or both. This type of construction will permit the blast wave from an internal explosion to spill over onto the exterior ground surface. These pressures, referred to as exterior or leakage pressures, once released from their confinement, expand radially and act on structures or persons, or both, on the other side of the barrier.

Conventional structures are designed to withstand roof snow loads of 30 pounds per square foot (1.44 kilopascals) and wind loads of 100 miles per hour (161 kilometers per hour). The loads equate to 0.2 pounds per square inch (psi).

Fragmentation Warhead

Common usage distinguishes between a gunshot wound and a shrapnel wound. More precise usage would term the later a fragment wound. Strictly defined, shrapnel means preformed fragments (the fragments exist already made within the explosive munition). Thus, fragmenrs from a random-fragmentation shell are not shrapnel. Also note that by strict definition, flechettes are shrapnel.

Naturally fragmenting warheads are primarily implemented in gun projectiles, mortar rounds and small rockets. These warheads are generally a compromise between cost and warhead case fragmentation performance. Although naturally fragmenting warheads are generally the least expensive method of high-volume warhead production, they usually do not fragment into the optimum fragment size for their given application or target set. For example, the target set for most gun-fired projectiles and mortar rounds includes personnel and other "light" targets such as trucks. Such applications generally require an optimum fragment size of approximately 15-30 grains. This fragment size is difficult to consistently achieve with naturally fragmenting warheads. Specifically, fragments are often too large which results in inefficient warhead performance.

A blast fragmentation type warhead is designed to destroy enemy missiles, aircraft, re-entry vehicles, and other targets. When the missile carrying the warhead reaches a position close to an enemy missile or other target, a pre-scored or pre-made band of metal on the warhead is detonated and pieces of metal are accelerated with high velocity and strike the target. The fragments of the blast fragmentation type warhead, however, are not always effective at destroying the target and biological bomblets and/or chemical submunition payloads can survive and still cause heavy casualties.

An important consideration in the analysis of explosions is the effect of the fragments generated by the explosion. These fragments are known as primary or secondary fragments depending on their origin. Primary fragments are formed as a result of the shattering of the casing of conventional munitions. These fragments usually are small in size and travel initially at velocities of the order of thousands of feet per second. Secondary fragments are formed as a result of high blast pressures on structural components and items in close proximity to the explosion. These fragments are somewhat larger in size than primary fragments and travel initially at velocities in the order of hundreds of feet per second. A hazardous fragment is one having an impact energy of 58 ft-lb (79 joules) or greater.

The study of ballistics, the science of the motion of projectiles, has contributed significantly to the design of fragmentation warheads. Specifically, terminal ballistics studies attempt to determine the laws and conditions governing the velocity and distribution of fragments, the sizes and shapes that result from bursting different containers, and the damage aspects of the bursting charge fragmentation.

Approximately 30% of the energy released by the explosive detonation is used to fragment the case and impart kinetic energy to the fragments. The balance of available energy is used to create a shock front and blast effects. The fragments are propelled at high velocity, and after a short distance they overtake and pass through the shock wave. The rate at which the velocity of the shock front accompanying the blast decreases is generally much greater than the decrease in velocity of fragments, which occurs due to air friction. Therefore, the advance of the shock front lags behind that of the fragments. The radius of effective fragment damage, although target dependent, thus exceeds consid-erably the radius of effective blast damage in an air burst.

Whereas the effects of an idealized blast payload are attenuated by a factor roughly equal to 1/R3 (R is measured from the origin), the attenuation of idealized fragmentation effects will vary as 1/R2 and 1/R, depending upon the specific design of the payload. Herein lies the principle advantage of a fragmentation payload: it can afford a greater miss distance and still remain effective because its attenuation is less.

Conventional bombs and warheads detonate in a manner that produces fragments of irregular size and shape. Fragments of nearly identical shape will disperse in a predictable pattern based on their orientation in the warhead and the configuration and method of detonation of the explosive charge in the warhead. Prior to construction of the warhead, the size and shape of the fragments must be determined, based on the desired warhead size and the object target - using standard techniques for determination of required kinetic energy for defeating the target and kinetic energy to be available in the fragment from the mass of fragment and explosive charge to be used.

Framentation warheads generally involve scoring or otherwise weakening the warhead casing, thus allowing a preferentail rupture at the weakened area and thereby causing some amount of blast concentration in the vicinity proximate to the weakened area of the casing. On detonation of the charge, shock waves strike the shell at differential increments of time, causing preferential fragmentation in the resulting shell burst. Configurations typically involve a single explosive burster charge surrounded by fragments, but because of low coupling efficiencies, a considerable amount of explosive was required if desirably high fragment velocities were to be achieved with a limited number of fragments.

To avoid random distribution of fragments propelled by exploding anti-property and personnel devices, it is necessary to control the size, shape, and weight of the fragments. Small fragments have low mass and will not possess optimum amount of kinetic energy against a desired target compared to a larger mass fragment traveling at the same velocity. Large fragments, and in particular, bar, plate, and diamond shapes, however, offer more atmospheric drag causing the fragment velocity to slow down rapidly, resulting in a reduced kinetic energy on the target. It can be appreciated that inconsistant fragment size, shape and weight are undesirable.

Heretofore, fragmentation control has included providing grooves on either the external or internal surfaces of the wall of the case or a liner inserted into the case. The grooves create stress concentrations that cause the case to fracture along the grooves forming fragments. Generally these grooves are longitudinal, circumferential, or both, or constitute a series of intersecting helical grooves designed to produce diamond shape fragments. While these devices have demonstrated the ability to create fragments, they are not completely satisfactory for several reasons.

First, the fragments are often much smaller than they ordinarily should be due to fragment weight loss during the fragmentation process. Allowance for weight loss requires that the device be designed to produce larger fragments than will actually result. This reduces the number of fragments available for a given warhead. Second, the prior art devices produce fragments of a variety of weights and do eliminate the variations in kinetic energy resulting therefrom. Additionally, diamond shaped fragments have high drag coefficients, which as stated, result in rapid decay of fragment velocity.

Casings that are relatively thick are susceptible to producing fragments of varying shapes and weights. The helical grooves heretofore utilized are ineffective in controlling these fragment variations. Finally, during the fragmentation process much energy is wasted on metal deformation. Frequently, the corners of the fragments are turned up which further increases drag. It is desirable to provide the device with means for increasing the amount of energy directed to fragmentation rather than being wasted in fragment deformation.

Fragmentation structures, such as fragmentation warheads, mines, etc., are employed by the military against a wide variety of targets where dispersion of fragments over a target area is required. A problem which arises in their use is that fragmentation warheads suitable for use against personnel are generally not suitable for use against "hard" targets such as armored vehicles and emplacements, where fragments of relatively greater size and mass are required. Military units have therefore been required to maintain supplies of several types of fragmentation warheads, each type adapted for use against a particular type of target. This results in an increased burden of logistics and supply and is, of course, highly undesirable.

It has been attempted to minimize this problem by constructing warheads having two sections, one section being adapted to disperse fragments of one size and the other being adapted to disperse fragments of another size. In this manner, a single warhead may be utilized against a variety of targets. Such a construction, however, is inefficient in that, in each case, portions of the warhead not designed for the particular application are largely ineffective; furthermore, in order to produce a given amount of destructive force, a warhead of larger dimensions is necessary than would be the case for one designed for the specific application.

Other problems related to the construction of fragmentation warheads have involved the expense of machining or casting a multiplicity of grooves or openings in the metal casings to induce fragmentation of the casing in a desired pattern by establishing preferential fracture lines. Alternatively, an inner casing having openings or grooves formed therethrough is disposed within an outer metal casing and configured such that it directs explosive shock waves from an internal explosive charge against the outer casing in a grid-like pattern, such that the outer casing is fractured along the grid lines. In all cases, the molding, machining, or forging of metal structures into a desired, grid-like pattern is undesirably expensive, particularly when large quantities of weapons are to be manufactured.

A further, related problem present with any explosive device is the danger of accidental detonation of the explosive charge by either mechanical shock or heat. Under combat conditions, for example, stored ammunition may be jarred by incoming rounds or careless handling, or it may be heated by fires started by incoming rounds. In any case, it is desirable that the ammunition be as resistant as possible to such heat and shock.

One prior approach to inducing fragmentation control to an integral warhead and missile structure has been to include grooves on either the external or internal wall surfaces of the structure to delineate fragments or projectiles in a combined warhead and missile structure. Explosives are installed in proximity to the grooves. When the explosives are detonated, the grooves create stress concentrations that cause the structure to fracture along the grooves, forming fragments. Generally, these grooves are longitudinal, circumferential, or both, designed to form rectangular fragments, or constitute a series of intersecting helical grooves designed to produced diamond shaped fragments.

Still another approach is the dual-wall naturally fragmenting (and combination natural fragmenting and scored wall) warhead. While these types of warheads have provided somewhat of an improvement over single-wall naturally fragmenting warheads, current dual-wall designs generally require thermal conditioning (i.e., both hot and cold temperature treatment) manufacturing methods to mate walls together with tight circumferential tolerances. However, the thermal conditioning processing steps are time consuming and expensive to implement.

Shrapnel

Common usage distinguishes between a gunshot wound and a shrapnel wound. More precise usage would term the later a fragment wound. Strictly defined, shrapnel means preformed fragments (the fragments exist already made within the explosive munition). Thus, fragmenrs from a random-fragmentation shell are not shrapnel. Also note that by strict definition, flechettes are shrapnel.

In application it has been shown historically that ammunition designed for the distribution of preformed fragments have been more effective against personnel and materials than explosive munitions dependant upon shell casing fragmentation for effectiveness. Typically this type of artillery munition consisted of thin walled frangible shells which were randomly filled with spherical shot and fired directly at a target, and were the predominate type used for hundreds of years.

In naval, coast defense and artillery operations, several types of explosive shells are used; the chief ones are: the armor-piercing shell, made to pierce armor plate before exploding; shells exploded by means of a timing fuse; shells exploded by either a timing or percussion fuse; and shells exploded by percussion only. Each different shell has some definite function to fulfill, and is designed for that purpose. For field or artillery operations, the shrapnel and lyddite are the two principal types used. Of these, shrapnel is the most prominent, because of its destructive power and its interesting mechanical construction.

The bursting charge may be located either in the front or in the rear of the shell, whose walls are thinner than in the case of ordinary shell. The bursting charge may also be contained in a central tube, as is the case of navy shrapnel, which may be larger than that used in field pieces. Shrapnel is designed for use against troops in open country or for clearing covered spaces, destructive effect over a considerable area rather than penetrative power being desired. With this in view the fuze is so adjusted that the projectile bursts in close vicinity to the target and scatters its fragments and the balls, which may be placed either in metal or wooden frames or plates or in a matrix of resin. In naval warfare shrapnel is used against attack by torpedo boats or small boats.

The shrapnel shell was invented in 1784 by Lieut. Henry Shrapnel, and was adopted by the British Government in 1808. This first shell was spherical in shape, and the powder or explosive charge was mixed with the bullets. Although this type of shell was an improvement over the grape and canister previously used, its action was not altogether satisfactory, as the shell, on bursting, projected the bullets in all directions and there was also a liability of premature explosion.

In order to overcome the defects mentioned, Col. Boxer separated the bullets from the bursting charge by a sheet-iron diaphragm. This shell was called a diaphragm shell to differentiate it from the first shell of this type. In the shell made by Col. Boxer, the lead bullets were hardened by the addition of antimony, and as the bursting charge was small, the shell was weakened by cutting four grooves extending from the fuse hole to the opposite side of the shell.

Shells of spherical shape were first fired out of plain-bored guns, and upon the advent of the rifled gun it was necessary to add a circular base, which was made of wood and covered with sheet iron or steel to take the rifling grooves. The first shrapnel shells were made of cast iron, but a later development was to use steel and elongate the body, reducing it in diameter. The diameter of the bullets was also reduced so that a greater number could be contained in a slightly smaller space. The improved shrapnel was also capable of being more accurately directed.

By the end of the nineteenth century shrapnel shells, as used by the different governments, varied slightly in construction and general contour as well as in the constituents entering into their different members. A completed shrapnel comprises a brass case carrying a detonating primer and the explosive charge for propelling the projectile out of the bore of the gun. The projectile itself comprises a forged shell that carries the lead bullets and bursting charge. Screwed into the front end is the combination timing and percussion fuse which can be set so as to explode the shell at any desired point, and from which the flame for exploding the bursting charge is conveyed through a powder timing train and a tube filled with powder pellets down through the diaphragm to the powder pocket.

A further improvement in the art was seen in U.S. Pat. No. 2,767,656 R. J. Zeamer in which the spherical shot was replaced with cylindrical slugs in closely arranged and stacked in self supporting vertical columns within a semi-frangible shell casing having a predefined release control. This was an improvement over similar munitions using spherical shot for target saturation with preformed fragments, but it lacked effectiveness in long-range applications.

An further improvement in the art was seen in the U.S. Pat. No. 3,956,990 John F. Rose in which the munition consisted of preformed fragments consisting of small finned darts, known in the art as flechettes, being assembled in round clusters and stacked within a semi-frangible shell body in layers separated by metallic disks and support rings. A base exploding charge activated by a fuse when the shell was in the proximity to the target dispenses the flechette clusters and support assemblies. This type of flechette packing has been the conventional standard for artillery and rocket munition use since it's invention.

Conventional fragmentation type of warheads, bombs, rockets and the like have an annular body with an explosive charge in the center and rows of fragments or rods assembled around the center and contained in a thin outer cylindrical casing, for example. Some designs employ a solid type structure surrounding the explosive core, which splits into fragments at specially weakened points when the charge is set off. To penetrate an armored target when the fragments are thrown out by the high explosive, such fragments are designed to have as high a ballistic coefficient as possible, achieved by high density material and low cross-section area in the direction of travel, and to have high explosive launch velocity.

Anti-personnel fragmentation munitions are designed to destroy or maim personnel or to damage material enough to render it inoperable. In the area of field artillery, the flechette or beehive round is an example of an anti-personnel warhead. The payload in this projectile consists of 8,000 steel-wire, fin-stabilized darts. Upon detonation the darts, or flechettes, are sprayed radially from the point of detonation, normally within sixty feet of the ground. It is extremely effective against personnel in the open or in dense foliage.

Armor-Piercing Projectile Armor-Piercing Projectile, known and abbreviated as an A.P. projectile, is one, as may be implied from the name, designed to pierce heavy armor plate, such as found protecting the vital parts of dreadnoughts. The depth to which this projectile will penetrate armor is greater than that of any other manufactured, but depends, of course, on the caliber of the projectile and velocity with which fired from the gun. A projectile fired from a high-power 14-inch gun will penetrate armor plate over 16 inches thick at a distance of 9000 yards. Armor serves two purposes: first, protection for the personnel, which involves that of the gun-positions and armament ; and, second, protection for the floatability and interior mechanism of the vessel. The latter includes protection of the hull and machinery. This protection is afforded to as great an extent as possible on early 20th Century warships by the armor-belt, extending the whole length of the ship, the side-armor and casemate-armor, the protective deck, turrets, barbettes, gun-shields, and armored conning-tovvers. For use against war vessels, by the end of the 19th Century forged steel projectiles were divided into shot and shell; the former ws a misnomer as the shot is really a shell, in that it contained a bursting charge. The only difference between the shot and shell is that the latter has a cavity accommodating a bursting charge approximately three times as large as that in the former. When these projectiles were first made, no explosive then known was sufficient in power to burst the shot, and the cavity was made merely for the purpose of obtaining a better forging. With the invention of Maximite, and later of Dunnite, for bursting charges, it was found that the shot could be exploded, and all armor piercing projectiles are now loaded with the bursting charge, and fuzed. At the end of the 19th Century only at shorter ranges can the belt armor of the heavier warships be pierced. At the longer ranges only the lighter armor can be pierced, but a sufficient number of hits, combined with the racking effect of the great bursting charge, would serve to put a warship out of action. For these longer ranges, then, the shell is used with its thinner walls, greater explosive charge, and an instantaneous fuse. At the near ranges, where actual perforation of the belt armor can be obtained, the armor piercing shot is used, with its heavy walls strong enough to stand the shock of impact, and supplied with a delayed action fuse which holds up the explosion of the bursting charge until the projectile has had time to penetrate to the vitals of the vessel. The earliest armor, both for ships and forts, was made of wrought iron, and was disposed either in a single thickness or successive layers sandwiched with wood or concrete. The first armor-piercing shell were designed by Sir W. Palliser, of England, and were made of chilled iron, or steel, with ogival shaped heads, a form combining strength and sharpness. They were filled with powder introduced through a hole in the base, which was subsequently closed by a strong screw- plug. They were fitted with percussion fuses, arranged to explode them the instant after impact. A 4.5-in. steel shield for the US government, face-hardened by the Harvey process, was attacked by 5-inch and 6-inch armour-piercing shot, and proved capable of keeping out the 5-in. up to a striking velocity of nearly 1,800 ft, per second, but was defeated by a 6-in. capped A.P. shot with a striking velocity of 1,842 ft. per second. Chilled iron, on account of its liability to break up when subjected to a continuous bombardment by the armor-piercing steel projectiles of guns of even medium calibre, was usually considered unsuitable for employment in inland forts, where wrought iron, mild steel or compound armor was preferred. On the other hand, it was admirably adapted to resist the few rounds that the heavy guns of battleships might be expected to deliver during an attack of comparatively limited duration. Chilled iron was never employed for naval purposes, and warship armor continued to be made exclusively of wrought iron until 1876 when steel was introduced by Schneider. As steel improved, efforts were made to impart an even greater hardness to the actual surface or skin of compound armour, and, with this object in view, Captain T. J. Tresidder, C.M.G., patented in 1887 a method of chilling the heated surface of a plate by means of jets of water under pressure. The inherent defect of compound armor, its want of homogeneity, remained, and in the year 1891 H. A. Harvey of Newark, N.J., introduced a process whereby an all steel plate could be face-hardened in such a way that the advantages of the compound principle were obtained in a homogeneous plate. The process in question consisted in carburizing or cementing the surface of a steel plate by keeping it for a fortnight or so at a high temperature in contact with finely divided charcoal, so that the heated surface absorbed a certain amount of carbon, which penetrated to a considerable depth, thus causing a difference in chemical composition between the front and back of the plate. Steel plates treated by the Harvey and Tresidder processes, which shortly became combined, possessed about twice the resisting power of wrought iron. The figure of merit, or resistance to penetration as compared with wrought iron, varied with the thickness of the plate, being rather more than 2 with plates from 6 to 8 in. thick and rather less for the thicker plates. In 1889 Schneider introduced the use of nickel in steel for armor plates, and in 1891 or 1892 the St Chamcmd works employed a nickel steel to which was added a small percentage of chromium. Krupp plates are made of nickel-chrome steel and undergo a special heat treatment during manufacture. The resisting power of the non-cemented Krupp plates is usually regarded as being considerably less than that of the cemented plates, and may be taken on an average to be 2-25 times that of wrought iron. At the time of the Great War manufacture of armor-piercing projectiles began with ingots of the necessary size and containing the required extra metal formed in projectile molds. The charge is made up of from 50 per cent to 75 per cent of pig iron or wrought iron (pig iron in open-hearth process, wrought iron in crucible process), metallic nickel, ferro-chromium, ferro-manganese, ferro-silicon, and projectile scrap, i.e., discard taken from the base ends of projectiles. Carbon may also be added, if necessary. After casting, ingots are reheated and forged to a desired form under a hammer, forging-dies being used. The blanks are then annealed to take out stresses, after which they are sent to the machine shop. From the machine shop the shells go to the treating-house, where they are specially hardened and where their bases are annealed. After final treatment the shells are subject to the immersion test in hot and cold water. Chemical and physical tests are made for the purpose of insuring- uniformity in each lot, and while not specifying the amount of carbon, nickel, or chromium, or other hardening element, a specimen from each heat is analyzed and the percentage determined, which is not permitted to vary more than a certain specified amount from the mean percentage of carbon, chromium, and nickel of the entire lot. By the time of the Great War practically all Naval projectiles above 7 inches in caliber were either armor-piercing or high-capacity, the armor-piercing having thick walls and being loaded with explosive "D," detonated by a delayed-action high-explosive exterior fuse called the Semple tracer detonator. The weight of the explosive, which is sufficient to fragment the shell, is from 2 to 3 per cent of the gross weight. A typical armor-piercing projectile had the same general dimensions and the ogival head and point described for projectiles in general. This point is extremely hard and well tempered. Over the ogival head and point is a cap. This is made of comparatively, soft steel and is rigidly secured to the projectile proper by an undercut score in the head. The end of the Cap is very blunt, little metal being in front of the point of the projectile. The theory or reason of the soft steel cap on armor-piercing projectiles is, that when fired, the entire weight of the projectile is utilized; first, to bend in the armor plate to a degree near its breaking point. In this process the soft steel cap is crushed down around the sides of the ogival head of the projectile. Now, inasmuch as the point of the projectile is very hard and sharp, the whole projectile continues its motion forward, the hard sharp point cutting right through the soft steel cap, striking, in a sense, another blow on the armor plate. The point of the projectile now pierces the already scaled plate and the projectile itself enters through and explodes in the rear of the armor plate, or on the inside of the vessel. The only difficulty in the satisfactory use of this soft steel cap now presents itself. The very blunt end or large flat area at the head of the projectile offers too much resistance to the air in its flight and therefore materially reduces the effective range. To overcome this difficulty there is screwed on to the blunt, forward end of the Cap another small, soft steel cap, this last cap being hollow. This cap is sometimes designated as a wind-shield for the reason that it brings the projectile practically to a point, and reduces to a negligible quantity the air resistance encountered by the blunt end of the Cap. It is also known as a thimble from its shape and its hollowness. It is made hollow in order that no metal be massed in front of the point of the projectile, which is objectionable, as has been explained before. At low striking velocities, probably in the neighbourhood of 1700 ft. per second, the cap fails to act, and no advantage is given by it 10 the shot. This is probably because the velocity is sufficiently low to give the cap time to expand and so fail to grip the point as the latter is forced into it. The cap also fails as a rule to benefit the projectile when the angle of incidence is more than 30 degrees to the normal. Projectiles striking armor at an angle of more than 10 from normal are subjected to severe cross-breaking stresses, and it is not expected that penetration will be effected under such conditions unless the projectile considerably overmatches the armor. Summing up on the use of the combined soft steel cap, the long, tapering cap gives a range equal to or greater than that attained by the ogival-headed projectile; gives a better trajectory to the projectile; and gives a considerably higher striking velocity at equal ranges than an uncapped projectile. By the time of the Great War it had been established beyond doubt, by exhaustive experiments, that under certain conditions capped shell may even pierce armor that has the balance of power, armor for which uncapped shells are no match under the same conditions. Although forms for caps which increase the efficiency of armor-piercing projectiles had been worked out in all nations in an empirical manner, there was no unity regarding theories as to the manner in which the caps attain their results. Deck piercing projectiles for coastal defense mortars wre similar to the armor piercing shell in that they had thin walls, and a large bursting charge, but are provided with a delayed action fuze, in order that the projectile may have penetrated the decks of a warship, including the protective deck, which covers the engine rooms and magazine, before the fuze operates to explode the bursting charge. Around 1900 the problem of penetrating the sides of armored vessels being so difficult, attempts were made to perforate their decks. When the weight of guns, machinery, and armor carried by ships of the day was considered, the available vyeight left for deck protection was comparatively small, and hence a thickness of about 4-1/2 inches of protective deck was about all that can be carried. Against these decks. the vertical fire of shell from heavy rifled mortars was directed. Since the thickness of plate to be penetrated was not great, the walls of the shell for these mortars need not be very thick, hence they have great interior capacity, carry heavy bursting charges, and their effect is very destructive. The disadvantage is, the difficulty of hitting the object ; but this is compensated for by increasing the number of mortars. High Explosive(HE)"; case 1100: return "HE, Plastic"; case 1200: return "HE, Incendiary"; case 1300: return "HE, Fragmentation"; case 1400: return "HE, Antitank"; case 1500: return "HE, Bomblets"; case 1600: return "HE, Shaped Charge"; case 1610: return "HE, Continuous Rod"; case 1615: return "HE, Tungsten Ball"; case 1620: return "HE, Blast Fragmentation"; case 1625: return "HE, Steerable Darts with HE"; case 1630: return "HE, Darts"; case 1635: return "HE, Flechettes"; case 1640: return "HE, Directed Fragmentation"; case 1645: return "HE, Semi-Armor Piercing (SAP)"; case 1650: return "HE, Shaped Charge Fragmentation"; case 1655: return "HE, Semi-Armor Piercing, Fragmentation"; case 1660: return "HE, Hallow Charge"; case 1665: return "HE, Double Hallow Charge"; case 1670: return "HE, General Purpose"; case 1675: return "HE, Blast Penetrator"; case 1680: return "HE, Rod Penetrator"; case 1685: return "HE, Antipersonnel"; case 2000: return "Smoke"; case 3000: return "Illumination"; case 4000: return "Practice"; case 5000: return "Kinetic"; case 6000: return "Mines"; Survivability is defined as the capacity of the ship to absorb damage and maintain mission integrity. The ability to effect major survivability improvements becomes difficult once the fundamental design trade-off decisions have been made. These decisions usually occur during the early design phases of the ship acquisition process. Since the installation of survivability improvements into existing ships has proven very expensive, a forward fit strategy is necessary to achieve high pay-off results. Focus on incorporating survivability features in the early phases of ship design will ensure an affordable balance of desired upgrades in the Top Level Requirements (TLRS) for each new ship class. Warships are expected to perform offensive missions, sustain battle damage and survive. As such, the total ship, comprised of combat systems and vital hull, mechanical and electrical components, must be sufficiently hardened to withstand designated threat levels. Enhancement techniques, such as equipment separation and redundancy, arrangements and personnel protection form an integral part of this effort. DC/FF training and associated maintenance of ship survivability features are also essential elements to ensure sustained capability. Survivability is considered a fundamental design requirement of no less significance than other inherent ship characteristics, such as weight and stability margins, maneuverability, structural integrity and combat systems capability. The Chief of Naval Operation's (CNO'S) goal is to maintain ship operational readiness and preserve warfighting capability in both peacetime and hostile environments. Ship protection features, such as armor, shielding and signature reduction, together with installed equipment hardened to appropriate standards, constitute a minimum baseline of survivability. These shall be implemented through appropriate ship and equipment specifications and the application of the principles of separation, redundancy and arrangements of critical components and systems. Major overhaul and modernization programs shall incorporate survivability enhancement features wherever practical and affordable. Survivability weapons effects and operational environments are categorized in terms of the three levels of severity described below. They provide a basis for establishing survivability performance standards and are not intended to describe conditions of readiness or misfin impact. Ship survivability features shall provide affordable protection to support sustained mission capability: Level I - low represents the least severe environment anticipated and excludes the need for enhanced survivability for designated ship classes to sustain operations in the immediate area of an engaged Battle Group or in the general war-at-sea region. In this category, the minimum design capability required shall, in addition to the inherent sea keeping mission, provide for EMP and shock hardening, individual protection for CBR, including decontamination stations, the DC/FF capability to control and recover from conflagrations and include the ability to operate in a high latitude environment. Level II - moderate represents an increase of severity to include the ability for sustained operations when in support of a Battle Group and in the general war-at-sea area. This level shall provide the ability for sustained combat operations following weapons impact. Capabilities shall include the requirements of Level I plus primary and support system redundancy, collective protection system, improved structural integrity and subdivision, fragmentation protection, signature reduction, conventional and nuclear blast protection and nuclear hardening. Level III - high, the most severe environment projected for combatant Battle Groups, shall include the requirements of Level II plus the ability to deal with the broad degrading effects of damage from anti-ship cruise missiles (ASCMS), torpedoes and mines. Semi-Armor Piercing (SAP) Common Shell Semi-Armor Piercing Warheads are designed to penetrate into the target and detonate, posing a blast/fragmentation threat to structures and vital systems. One predominant class of threat weapon in the early 21st Century is the anti-ship cruise missile carrying a semi-armor piercing warhead designed to penetrate the hull and detonate inside. It creates a shock wave and a large amount of high-pressure gas. When contained, this can rupture bulkheads and doors, expanding the damage area, allowing fire and flooding throughout the ship. The loading may rupture bulkheads by causing the connection to the deck to fail, forcing it out of the way. The use of commercial construction practices may affect the pressure at which the bulkheads fail because the connection details are different. A common shell is a hollow cylindrical casting having an ogival head. The term came into use in the early 19th Century, and remained in use through the early 20th Century. Common shell have been made of cast-iron, cast-steel, and forged-steel. The forged-steel shell, being tough and having good penetrating power, has sometimes been called "the semi-armor-piercing shell." The term common shell was preferred by the early 20th Century US Navy, however. The US Navy differerntiated between the common shell and high explosive shell, the later having a higher proportion of explosive fill and a corresponding thinner case. By 1898 five kinds of projectiles were used in the US Navy - armor-piercing, semi-armor-piercing, common cast-iron, shrapnel, and canister. With the exception of canister, all other shells contain bursting charges, but naturally the bursting e'ect of the semi armor-piercing shells is much greater than that of the armor piercing. In an attack upon earthworks the semi-armor-picrcing shells would be used ; while against unarmored ships common shell and shrapnel would be employed. In an attack upon an ironclad possessing no unannored superstructures (monitors), armor-piercing shells would be used exclusively; but when opposing battleships, which present large unarmored surfaces, both kinds of shells may be employed. Some guns whould be loaded with armor-piercing and others with semi-armor-piercing shells. When semi-armor-piercing shells strike armor, they do not pierce it, but when they strike unarmored parts they do more injury than the armor piercing. If an antagonist possesses no thin armor, but only heavy plates, medium-caliber guns, which are unable to pierce thick armor, would be loaded exclusively with semi-armor- piercing shells. In the early 20th Century three kinds of projectiles were in use in the U.S. Navy for the large caliber guns : Armor-piercing, common or semi-armor piercing, and shrapnel. As a rule the latter would only be used in the attack of exposed bodies of men. The specifications for the former require that armor-piercing shell shall perforate face-hardened armor-plate of thickness equal to the caliber, and remain in a condition for effective bursting. Semi-armor piercing, or forged-steel shell, must pass through half a caliber of face-hardened armor and remain in a condition for effective bursting. Armor-piercing projectiles of the early 20th century were made solid, or practically so, a small core being formed to give the best results in the forging process. The semi-armor-piercing was formed hollow, with a core of moderate dimensions, large enough to hold an explosive charge that will insure the bursting of the thick walls of the projectile. It is made of chrome steel, and requires in its manufacture to be treated with great care to secure the combined hardness and toughness to enable it to pierce solid armor without fracturing and carry its explosive charge intact into the interior of the ship. When such shell is filled with common powder the heat engendered by passing through the armor is depended on to explode the shell just within the ship; no fuse was used. A common shell is filled with powder which forms the bursting charge, and is fitted with either a time or percussion fuze, according to the nature of ordnance from which it is fired. The use of this shell is for all purposes where great destructive effect is required, such as against men in masses, buildings, shipping, and material generally, either by bursting during flight or at rest, when the shell acts as a mine. It is used particularly in the field when the enemy is sheltered from direct fire, or against cavalry to frighten the horses and create confusion. In the early 20th Century warship provided one thickness of armor for protection against armor-piercing projectiles and another for defense against common shell. At the battle of Tsushima there was not only no penetration of the heavy armor, but even the light armor was pierced on extraordinarily few occasions taking into account the enormous number of hits (the case of the Orel, for example). The same thing was observed in the Chino-Japanese war, at the battle of the Yalu, and in the Spanish-American war at Santiago. For the moment, the penetration of armor seemed unattainable with present equipment. Russian war experience in 1904 showed that a common shell, even if it strikes on the most heavily armored part, sets up such a concussion that the protecting armor is shattered and cracks appear in the side of the ship, through which water is irresistibly forced. A very good example of this was the Retvizan which on February 26, 1904, was hit by five common shell, one of them striking on the most heavily armored part near the waterline, at a range of nine miles; the armor was not pierced, but the concussion was such that a leak appeared which was overcome only with the greatest difficulty. Hits from armor piercing and common shell may be easily distinguished also in the lightly protected parts by the difference in the damage inflicted. The common shell causes damage over a surface of 100 square feet, driving into the ship rivets and portions of the hull. Besides this it discharges an immense amount of gas heated to an enormous temperature which consumes everything, and envelopes the ship for quite a long time in a dense suffocating atmosphere. The armor piercing shell with its small bursting charge produces a comparatively slight effect, for even if it does penetrate, it makes an exceedingly small hole and as its burst takes place after penetration, the only effect is a shower of splinters. From these considerations, it would appear that the only possible projectile against a ship is the common shell with instantaneous fuze, as its effect extends over the whole surface of the ship, and does not depend either on the angle of impact or on the range. This then is one consideration which will influence the choice of weapon for coast armaments. Before the Great War the study of projectiles in France and Germany developed from different definitions of effectiveness. A fragment was effective, according to French definitions, when it passed through a pine panel 41 mm. thick. In Germany the standard thickness was much less (about one-half). It will easily be understood that different types of shell developed in the two countries. The German shell does not pass through a plate of special steel 20 mm. thick. To fight tanks the Germans therefore developed a special projectile. This projectile is derived from the model 1915 explosive shell which was transformed into a semi-armor-piercing shell. A massive ogive of hard steel is screwed on the shell body, which has been duly adapted to receive it. The front of the ogive terminates in a flat nose 20 mm. in diameter. At the bottom of the cavity is a metal box containing a smoke-generating substance. This box is separated from the explosive by a layer of pitch. In the early 20th Century the US Army classified shells as common shell and high explosive shell. The US Army's common shell [which was more or less obsolete at that time] was a hollow cast-iron cylinder with an ogival head and contains a bursting charge of black powder. The high explosive shell is of practically the same shape and dimensions as the common shell, but was made of steel and contains a bursting charge of high explosive (a picric acid compound). The bursting charge in both the common and high explosive shell is exploded by percussion fuse. Either shell may be characterized as a flying mine, the chief object of which is to destroy material objects at a distance, although either may be used effectively against troops. The standard design for metal-piercing ammunition includes a hardened steel penetrator encased by a soft metal jacket to prevent damage rifling in the base of the weapon as the ammunition is discharged. The jacket is usually composed of a soft metal called gilding metal while the nose or piercing end is steel or some other hard metal. The jacket also operates as a windshield by reducing aerodynamic drag thereby control the amount of energy lost between the nozzle of the gun and the target. In the 21st Century, General-purpose (GP) bombs are used against unarmored ships or ground targets for blast or fragmentation. Fragmentation bombs are very small explosives dropped in clusters against troops and ground targets. Semi-armor-piercing (SAP) bombs are used against carriers, cruisers, and "hardened" ground targets. High-Capacity Shells High-capacity shells have the same external appearance as an armor-piercing projectile without a soft steel cap. These shells are made for large-caliber guns only, and are designed, not to pierce heavy armor plate, but to destroy the upper works of battleships and pierce comparatively thin armor. With this end in view the walls of the shell are made thinner than those of armor-piercing projectiles and the seat of the bursting charge very much larger. In the United States at the beginning of the 20th Century the bursting charge consisted of "Explosive D" and weighs up to 10% of the entire weight of the projectile, as compared with a relative weight of from 2% to 3% of bursting charge in an armor-piercing projectile. High-capacity shells are otherwise fitted with base plugs, fuses, tracers, etc., of the same types as armor-piercing projectiles of corresponding calibers. Prior to the Great War, it had been apparent to the US Navy that naval guns might be called upon to participate in land operations, either by actual bombardment by the fleet or by use of naval guns ashore, and the design of suitable projectiles was developed. Immediately that funds were available therefor, the Bureau of Ordnance, in March 1917, contracted for a supply of approximately 3,000 special high capacity, high-explosive projectiles, for the Navy's standard 14-inch guns; and the delivery of this entire order was completed in December, 1917. The wisdom of this move was later demonstrated, when the Navy railway battery was proposed, and these projectiles were used in France by that battery. It is interesting, in this connection, to note that the Navy turned over to the Army approximately 50 per cent of these projectiles, which number was in excess of the Navy's needs for its own batteries, for use in similar guns. Similarly, it was decided that a high capacity, high-explosive projectile would be exceedingly effective for the high power 7-inch naval guns which were being made available for use ashore, and, on April 25, 1918, the bureau placed orders for a considerable quantity of such projectiles. Within one month of the placing of this contract, deliveries of projectiles had commenced. These projectiles were assigned to the 7-inch tractor mounts, when that project was launched. This type of projectile was exceedingly useful for such purposes and gave excellent range qualities. BLIND OR TARGET projectiles are made of cast steel or cast iron. They have the external appearance of a capped armor-piercing projectile. The only use of these projectiles is in target practice. The cavity is filled usually with sand, but can be filled with any substance which will give the shell the desired weight. These projectiles are never fitted with fuses and have no bursting charge, but do have tracers when used in night practice. They are essentially "blind" or "dummy" shells; their only requisites being shape and weight. When the bomb Is released from the plane a pin on the release mechanism is caught in the loop of the safety wire, thus withdrawing the other end from the hole in the safety pin. The action of the spring throws off the safety pin, which releases the detonator. As soon as the bomb has assumed a vertical position the detonator slides forward. Its forward movement, however, is retarded by the cushion of air underneath it, there being but little clearance between the detonator and the booster cup tube. In this manner the detonator Is seated gently on the lead safety pin. When the bomb comes in contact with any object the detonator Is driven forward by inertia, the lead pin is bent or crushed, and the primer strikes the firing pin. The flash from the primer Ignites the black-powder train, this explodes the fulminate, which is now inside the booster cup. The booster charge is thus detonated, in turn detonating the main charge. The high-capacity drop bomb, Mark II, is provided with a special front cap and auxiliary safety wire, in order that it may also be used in connection with the vertical release mechanism. The shell cap Is similar in shape to those on the Mark I and Mark III. It is a steel cone, 15/16 of an inch high and 2.13 inches at its largest diameter. A cylinder 3/16 of an inch long projects from the base of the cone, and is threaded to a diameter of 1-3/8 inches to fit into the front bushing. At a point 1/2 inch from the front end a recess is cut around the conical portion/ 1/4 of an inch wide and 1 inch in diameter, to receive the jaws of the release mechanism. A hole 3/16 of an inch in diameter and 1/4 of an inch deep is drilled into this surface to provide a grip for a wrench.

Shaped Charge

The discovery of what is variously referred to as the shaped charge effect, the hollow charge effect, the cavity effect, or the Munroe Effect, dates back to the 1888 in the US. Dr. Charles Munroe, while working at the Naval Torpedo Station at Newport, Rhode Island, in the 1880s, discovered that if a block of guncotton with letters countersunk into its surface was detonated with its lettered surface against a steel plate, the letters were indented into the surface of the steel. The essential features of this effect were also observed in about 1880 in both Germany and Norway, although no great use was made of it, and it was temporarily forgotten.

Charles Munroe (1849-1938), the inventor of smokeless gunpowder, was head of the Department of Chemistry and the Dean of the Corcoran Scientific School at Columbian University (which became George Washington University in 1904.) between 1892 and 1898. Munroe was considered one of the world's authorities on explosives, and authored more than 100 books on that subject, as well as chemistry. He was the recipient of numerous honors from governments and scientific societies, including an appointment in 1900 by the Swedish Academy of Science to nominate the candidate for the Nobel Prize in chemistry. Munroe served as president of the American Chemical Society and fellow of the Chemical Society of London. Domestically, he was a consultant to the US Geological Survey and the US Bureau of Mines.

Von Foerster was the true discoverer of the modern hollow charge [Hohlladung]. A pair of Swiss inventors were the first to think of using the well documented Munroe Effect to penetrate armor plate. They tried to sell the design to foreign arms manufacturers, claiming that a new explosive had been discovered. Unfortunately for the inventors, explosives experts soon figured out that a shaped charge was responsible for the amazing penetration results, and they went ahead and copied it. The United States was the first to use these shaped charge in the late 1930's as an anti-tank weapon; the Soviet Union, Germany, and Great Britain followed as early as 1940. The worlds first anti-tank weapon using the hollow charge was the German "Panzerfaust" [Armoured fist].

A shaped charge warhead consists basically of a hollow liner of metal material, usually copper or aluminum of conical, hemispherical, or other shape, backed on the convex side by explosive. A container, fuze, and detonating device are included.

When this warhead strikes a target, the fuze detonates the charge from the rear. A detonation wave sweeps forward and begins to collapse the metal cone liner at its apex. The collapse of the cone results in the formation and ejection of a continuous high-velocity molten jet of liner material. Velocity of the tip of the jet is on order of 8,500 meters per sec, while the trail-ing end of the jet has a velocity on the order of 1,500 meters per sec. This produces a velocity gradient that tends to stretch out or lengthen the jet. The jet is then followed by a slug that consists of about 80% of the liner mass. The slug has a velocity on the order of 600 meters per sec.

The penetration depth of the jet depends on the length of the jet upon impact, and its relative density towards that of the target material. Since the jet stretches during its flight, a better performance is obtained using a standoff between the perforating charge and the target. At larger standoff, the jet is broken into many small particulates that show much less penetrating power than a continuous jet.

When the jet strikes a target of armor plate or mild steel, pressures in the range of hundreds of kilobars are produced at the point of contact. This pressure produces stresses far above the yield strength of steel, and the target material flows like a fluid out of the path of the jet. This phenomenon is called hydrodynamic penetration. There is so much radial momentum associated with the flow that the difference in diameter between the jet and the hole it produces depends on the characteristics of the target material. A larger diameter hole will be made in mild steel than in armor plate because the density and hardness of armor plate is greater. The depth of penetration into a very thick slab of mild steel will also be greater than that into homogeneous armor.

In general, the depth of penetration depends upon five factors:

  • Length of jet
  • Density of the target material
  • Hardness of target material
  • Density of the jet
  • Jet precision (straight vs. divergent)

The longer the jet, the greater the depth of penetration. Therefore, the greater the standoff distance (distance from target to base of cone) the better. This is true up to the point at which the jet particulates or breaks up (at 6 to 8 cone diameters from the cone base). Particulation is a result of the velocity gradient in the jet, which stretches it out until it breaks up.

Jet precision refers to the straightness of the jet. If the jet is formed with some oscillation or wavy motion, then depth of penetration will be reduced. This is a function of the quality of the liner and the initial detonation location accuracy. The effectiveness of shaped charge warheads is reduced when they are caused to rotate. Spin-stabilized projectiles generally cannot use shaped-charge warheads.

Pyrotechnics

Pyrotechnics are typically employed for signaling, illuminating, or marking targets.

  • Illumination--These warheads usually contain a flare or magnesium flare candle as the payload, which is expelled by a small charge and is parachuted to the ground. During its descent the flare is kindled. The illuminating warhead is thus of great usefulness during night attacks in pointing out enemy fortifications. Because these flares are difficult to extinguish if accidentally ignited, extreme caution in their handling is required.
  • Smoke--These munitions are used primarily to screen troop movements and play a vital role in battlefield tactics. A black powder charge ignites and expels canisters that may be designed to emit white, yellow, red, green, or violet smoke.
  • Markers--White phosphorus is commonly employed as a pay-load to mark the position of the enemy. It can be very dangerous, especially in heavy concentrations. The material can self-ignite in air, cannot be extinguished by water, and will rekindle upon subsequent exposure to air. Body contact can produce serious burns. Copper sulphate prevents its re-ignition.

Cluster

Cluster munitions are canisters containing dozens or hundreds of small bomblets for use against a variety of targets, such as personnel, armored ve-hicles, or ships. Once in the air, the canisters open, spreading the bomblets out in a wide pattern. The advantage of this type of warhead is that it gives a wide area of coverage, which allows for a greater margin of error in delivery.



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