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Torpedoes

The first successful implementation using a self-propelled vehicle to carry the charge to an enemy at some distance was the work of an Englishman, Robert Whitehead, who managed an iron works in Fiume, an Austro-Hungarian port city at the head of the Adriatic Sea. In 1866, he produced the first working "automobile torpedo," powered by compressed air and capable of carrying an 18-pound dynamite charge for 700 yards at six knots. Just before the end of the 19th Century, an Austrian, M. Ludwig Obry, adapted the gyroscope to the torpedo for directional control, and in a series of improved versions, the Whitehead torpedo was quickly adopted by navies worldwide for use on small, fast "torpedo boats" intended for attacking capital ships.

Vickers, Ltd. in England, revolutionized torpedo propulsion by devising an alcohol-burning "steam" torpedo powered by a small turbine. This innovation yielded higher speeds and much longer ranges, and in 1907, the U.S. Navy built a factory at the Torpedo Station specifically to produce an American version of the British weapon. Adding their own improvements notably injecting water into the combustion chamber for more steam U.S. engineers scaled the resulting "Bliss-Leavitt" torpedo up to 21-inch diameter to yield a weapon that could travel at 36 knots to a range of 3,500 yards.

New, higher-energy torpedo propellants were also studied, because of the great increases they offered in speed and range. Most important of these were the so-called "oxygen" systems that used the decomposition of concentrated hydrogen peroxide to generate an oxidant for the primary fuel. This approach was adopted successfully by the Japanese before the war for both submarine and surface-ship torpedoes, among the latter, the infamous 24" "Long Lance," which emerged as the most effective destroyer torpedo of the conflict. However, because of concern about the dangerous volatility of the associated fuels and oxidizers, the U.S. Navy delayed its acceptance of this approach until the early years of the Cold War, when variants were adopted for the Torpedoes Mark 46 and Mark 48.

The battery-powered Torpedo Mark 44, first introduced in 1956, and its widely-deployed successor, the Torpedo Mark 46, which first appeared in 1963 using solid chemical fuel, but then modified in 1967 to employ liquid monopropellant. Honeywell/Alliant Tech developed the Torpedo Mark 50 formerly the Advanced Lightweight Torpedo which was fielded in limited numbers in 1994 employing a Stored Chemical Energy Propulsion System (SCEPS) based on a lithium-flourine reaction to achieve high speed and deep diving capability.

The MK48 Advanced Capability (ADCAP) Heavyweight Torpedo, along with the MK46 Mod 5 and the MK50 Lightweight Torpedoes, are currently the workhorses of the fleet. The heavyweight torpedo is the submarine's key multi-mission underwater weapon, capable of performing both anti-submarine and anti-surface roles. The MK48 Mod 5, with its improved guidance system, and the MK48 Mod 6 with low-noise propulsion, provide the fleet with torpedoes whose performance is unmatched in deep-water scenarios. The lightweight torpedo gives surface ships, airplanes, and helicopters the means to destroy threat submarines. The MK54 Lightweight Torpedo will bring considerably improved shallow water capabilities to the fleet in 2003. Building on the success of the ADCAP torpedo, new weapon technologies are being developed to tackle the challenging shallow-water littoral environment. These technologies will be common to both the heavyweight and lightweight torpedoes to keep costs down and maximize performance across the board.

Since the end of the Cold War, submarine missions have largely moved from deep water to shallow-water littoral areas. Acoustic reverberation, poor sound propagation, local ship traffic, false targets, and bottom clutter all make torpedo operations more difficult in this noisy operating environment, and the need for more capable guidance and control becomes critical. The Common Broadband Advanced Sonar System (CBASS) upgrades to ADCAP will extend the current sonar array on the weapon into a broadband mode and improve the onboard signal processing to provide enhanced operation against countermeasures and diesel submarines operating in the littorals.

The Office of Naval Research (ONR) is supporting new, advanced technologies to solve emerging fleet problems by developing and delivering solutions to the operators in the shortest possible time. One new prototype torpedo, developed as part of their "Swamp Works" effort, will house an ultra-broadband, multi-beam array, which in conjunction with new waveforms, signal processing algorithms from the CBASS program - and improved torpedo tactics - will allow for greatly improved countermeasure rejection in shallow water, while maintaining current performance in deep water.

Developing a truly stealthy torpedo will provide more approach-and-attack options for submarines. A stealth weapon that cannot be heard until very late in the encounter will delay the threat's detection of the torpedo and impair its ability to respond effectively with either countermeasures or return fire. This will greatly increase the probability of killing the enemy and avoiding a potentially lethal counterattack.

The MK48 Mod 6, while a quiet weapon, still alerts a target when it begins active pinging at the "enable" point. To solve this problem, gthe Navy developed advanced passive homing techniques, covert active waveforms with LPI (Low Probability of Intercept) and LPR (Low Probability of Recognition) properties, and associated signal processing. To fully exploit these enhancements, however, a further reduction in radiated noise from the propulsion system is required. Under consideration for the stealth torpedo is a quiet electric or hybrid propulsion system employing the Integrated Motor Propulsor (IMP). The IMP incorporates a radial-field electric motor directly into the torpedo propulsor, thereby completely eliminating an internal motor, through-hull shafts and seals, and creating a single connection point to the hull, where advanced isolation can be utilized for increased stealth. This closed-cycle propulsion will be quiet, wakeless, and depth-independent. And, with a rechargeable energy source, it will help reduce exercise expenses to provide more training opportunities and/or lower total ownership cost. Additional quieting will be achieved using active noise-cancellation techniques.

Torpedo tubes are usually limited to 4 and are situated in the fore end of the submarine with a complicated system of tanks used to fire the torpedoes and compensate the weight of these with sea water. The torpedo room is located behind these tubes. Space considerations limit the capacity of most American SSNs to about 22 weapons. With the advent of submarine-launched air cruise missiles such as Tomahawk and Harpoon, this capacity was insufficient to ensure an adequate mix of weapons and guarantee the submarine a sufficient minimum number of each type of weapon to meet many mission requirements. In addition, due to the nature of the tactics involved in the use of air cruise missiles (particularly against heavily defended surface ships), there was a need to be able to fire more of these weapons quickly. The 688I class of attack submarines solved this problem by incorporating a Vertical Launch System (VLS) consisting of 12 tubes mounted vertically in the forward MBT area and dedicated exclusively to carrying air cruise missiles. Each tube carries one round and can only be reloaded when the submarine is docked. The new Seawolf class SSNs solves the problem by having 8 torpedo tubes and a capacity of about 48 weapons with the added advantage that these are general purpose tubes which can fire a full range of attack submarine weapons, thus permitting greater flexibility in configuring the weapons mix.

Unfortunately, this increase in weapons-carrying capacity is one of the reasons for the tremendous increase in the size and cost of attack submarines: whereas a Sturgeon class boat displaces some 4700 tons submerged, a 688 displaces 6900 tons and the Seawolf around 9100 tons.

Reloading torpedoes is a rather long process which, in the case of a 688 class submarine, involves dismounting part of the interior floor space to assemble a ramp mechanism on the deck so that weapons can be lowered on a slide to the torpedo room and placed on their respective racks. The entire process of reloading a full weapons load is reputed to take some 12 hours.

Firing a weapon from a torpedo tube also takes rather longer than is desirable. First the weapon must be loaded into the tube and the electrical signal connections made. The breech is closed and water from the Water Round Torpedo (WRT) tank is used to fill the space between the torpedo and the tube. The torpedo is "tested" by the fire control team to ensure it is in working order and the relevant targeting instructions are transmitted to the guidance system. Pressure is equalized with surrounding sea water by opening a slide valve and, finally, the pressure cap and exterior doors are opened and the torpedo can be fired. Once fired, the tube remains filled with water which partly compensates for the weight of the weapon. However, as the weapon is usually heavier than the water it displaces, in order to maintain trim, the Automatic Inboard Venting tank must take on sufficient water to compensate for the difference.

If the weapon fired is a wire-guided torpedo, the tube cannot be reloaded unless the decision to cut the wire is taken. Reloading a torpedo tube takes even longer. The muzzle cap and slide valves must be closed and the water from the tube drained into yet another tank called the Torpedo operating Tank situated where it can continue to maintain longitudinal balance and with sufficient capacity to take on all the water required to compensate for the loss of weight which would result if a full load of weapons were discharged. The breech door can now be opened and the tube inspected and cleared of any remaining wires and dispensers before the crew can proceed to reload a new weapon.

There are a number of additional disadvantages to forward-mounted torpedo tube arrangements:

The process of preparing a tube for firing and then actually firing the weapon results in a large amount of noise being generated in the vicinity of the bow sonar which is the main sonar array. This noise causes the sonar to be temporarily "blinded". Furthermore, firing a torpedo from the bow implies having to give it sufficient impulse to overcome the forward speed of the submarine and to ensure that the submarine will not hit the torpedo should its engine fail to start.

Wire-guided torpedoes require that the doors of the torpedo tubes remain open until the wire runs out or the decision is taken to cut it. Since this wire can be over 10 miles long, the submarine may be manoeuvring for a long while with open doors near the bow area which cause a certain amount of turbulent noise. There is also a risk that the wire may rub over the bow sonar casing thus causing more interference.

The acute angles the guidance wire may take with respect to the tube muzzle or the hull door opening may cause the wire to break, particularly during evasive manoeuvres. To reduce this possibility, some torpedoes have a wire dispenser which is attached to the breech end of the tube in addition to a dispenser at the stern of the torpedo. The wire is paid out from both ends in order to reduce its tension. Additional protection for the wire is usually provided by a reinforced "flexhose" which extends through the tube and outside the hull and through which the guidance wire runs. However, there is a risk that this flexhose could later interfere with the closing of the tube pressure cap or hull door.





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Page last modified: 26-12-2019 18:27:47 ZULU