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Artillery Caliber - 39-caliber vs 52-caliber

Where artillery dimensions are concerned, caliber is the multiple of the length of a gun barrel compared with its diameter; hence a 39-caliber gun is 39 times as long as it is wide. The quest for longer range is probably as old as cannons themselves. Increased range enables the weapon to cover a larger portion of the enemy target array, gives artillery units greater ability to provide fires for neighboring formations on their flanks, and improves the survivability of cannon units by permitting the guns to stand well back from the front lines, thus inhibiting the ability of at least some enemy systems from ranging the friendly gun positions.

The current generation of SPHs becoming available in the world today are most often 155mm, with some 152mm weapons still being produced in the former Soviet bloc. Weapons of 39, 45, and now 52 caliber have become the standard. When employing base-bleed or rocket-assisted projectiles (RAP), these weapons can easily achieve ranges of 30-45 kilometers. Some howitzers are in the process of being refitted with longer-barreled weapons to extend their ranges. For example, the original version of the British AS 90 was armed with a 39-caliber tube (maximum range of approximately 30 kilometers with rocket-assisted munitions). The British army sought to reequip its artillery regiments with 52-caliber tubes that will permit ranges of approximately 40 kilometers.

The primary howitzers of the U.S. military are the M109A6 and M777. The ammunition and powder utilized by these two weapons platforms is standardized and features a variety of shell/fuze combinations including: high explosive (point detonation/air burst), smoke, white phosphorous, illumination, area denial munitions, rocket assisted projectiles, and improved conventional munitions. All of the aforementioned munitions are not precision guided and are fired using conventional fire direction control methods.

Both weapon systems have a .39 caliber gun tube which provides for a range of 24 km for HE and other conventional rounds and 30 km for rocket assisted projectiles, while precision guided munitions can range out to 40 km. With its 39-caliber tube, the Paladin is limited to a range, with rocketassisted projectiles, of 30 kilometers—a range that is clearly on the low end of the capabilities of the modern generation ofself-propelled weapons. Currently, the Army does not plan to refit Paladin with a longer gun tube. Such a modification could further strain Paladin's chassis and power plant, both of which are already near maximum capacity.

Longer and more powerful 52-caliber guns have longer barrels and larger chambers, which permits more-powerful charges to be used. The 39-caliber 155-mm gun on Paladin (and also on the M198 and M777 towed howitzers) has an 18-liter chamber, which can accommodate less propellant than the (generally) 23-liter chambers of 45-caliber and 52-caliber guns that are in wide circulation elsewhere in the world. Medium self-propelled howitzers that outrange Paladin while firing standard ammunition are increasingly common. While Paladin can make up some of the range gap using Excalibur, this requires the use of an expensive round that is fielded only with a unitary warhead; the disadvantage of Paladin’s shorter range while employing special ammunition types, such as smoke or illumination rounds, remains.

The Caesar’s 52 caliber cannon allows it to achieve a range of over 40,000 meters with conventional ammunition, and it can store 18 complete rounds right on board the vehicle. The 52 caliber cannon allows for future range increases as 155mm ammunition technology improves, which would not be possible with the 39 caliber cannon on the M198 or M777.

While the more powerful 45- and 52-caliber guns have been adopted with increasing frequency in self-propelled howitzers, these are less common among towed guns. The 155/52 APU SBT has been fielded in relatively limited numbers (around 80) by Spain and Colombia. Guns similar to the 155/52 APU SBT have been fielded in Singapore (FH2000), Turkey (Panter), and Finland (GH 52) in smaller numbers. Some of the more powerful Russian 152- mm guns, such as the 2A36, have similar characteristics but appear to lack a comparable suite of projectiles that would enable them to engage targets beyond 35 km.

The American XM-2001 Crusader self-propelled howitzer used a 56-caliber barrel (56 times the 155mm diameter of the howitzer). The Advanced Field Artillery System (AFAS) was a 155-millimeter self-propelled howitzer designed for the battlefield environment of the next century. This system is to offer a notable increase in mobility, survivability, and lethality over the Ml09A6 (Paladin), the present system. The Army developed the XM-230 Unicharge propellant and 56 caliber XM-297 Cannon as back-up risk mitigation efforts for AFAS / Crusader. The US Army remained committed to the Crusader prior to its cancellation in May 2002.

ARDEC is pursuing a next generation howitzer under the Extended Range Canon Artillery (ERCA) program. The goal of ERCA is to develop a 52-caliber 155mm gun system that weighs the same as a 39-caliber system. This requires the use of new materials such as high-strength steel and composites. Of specific interest are Nextel 610 (Al2O3) fibers in a cast aluminum matrix, with the goal of casting the MMC directly onto the steel gun barrel. Specific areas of manufacturing research include challenges with keeping the steel substrate below its thermal soak temperature, formation of intermetallics at the interface, and galvanic corrosion between the steel and aluminum.

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Page last modified: 31-05-2019 14:53:33 ZULU