155 mm gun M1


The 155 mm gun M1 was a 155 millimeter caliber field gun developed and used by the United States military. Nicknamed "Long Tom", it was produced in M1 and M2 variants, later known as the M59. Developed to replace the Canon de 155mm GPF, the gun was deployed as a heavy field weapon during World War II and the Korean War, and also classed as secondary armament for seacoast defense. The gun could fire a shell to a maximum range of, with an estimated accuracy life of 1,500 rounds.
The Long Tom was also adopted by a number of other nations, including the United Kingdom, Austria, Israel, and the Netherlands.

Development

Before entering World War I, the United States was poorly equipped with heavy artillery. To address this problem a number of foreign heavy artillery guns were adopted, including the Canon de 155 mm GPF. After the end of the war the Westervelt Board was convened to assess the artillery experience of the combatant powers and map out future directions for the US Army artillery. The conclusion of the board vis-a-vis heavy field artillery was that the French 155mm GPF should be adopted as the standard heavy field piece but further development work should occur to achieve a heavy field gun with a max. range of 25,000 yards, a vertical arc of fire from 0° to 65°, a projectile not exceeding 100 lbs and the capability to be mounted on a caterpillar mount or a rubber tired towed mounting. A number of prototypes were produced in the 1920s and 1930s, but the projects were put on hold due to lack of funds. In 1938 the 155 mm gun T4 on carriage T2 was finally adopted as 155 mm gun M1 on carriage M1.

155 mm gun M1

The new gun design used a barrel similar to the earlier 155 mm GPF, but with an Asbury mechanism that incorporated a vertically-hinged breech plug support. This type of breech used an interrupted-thread breech plug with a lock that opened and closed the breech by moving a single lever. The ammunition for the 155 mm gun was "separate-loading", that is with the shell and the powder charge packaged, shipped and stored separately. The shell is lifted into position behind the breech and then rammed into the chamber to engage the shell's rotating band into the barrel rifling.
Ramming the shell home is followed by loading a number of powder bags, as required for the desired range. The powder charge could be loaded in up to seven charge settings. Once the powder is loaded, the breech plug is closed and locked, and a primer is placed in the breech plug's firing mechanism. After setting the elevation and azimuth, the gun is ready to fire. The firing mechanism is a device for initiating the ammunition primer. The primer then sets off the igniter which ignites the propelling charge of the ammunition. A continuous-pull lanyard first cocks the firing pin, then fires the primer when pulled.
The gun was developed into M1A1 and M2 variants. After World War II, the United States Army re-organized, and the gun was re-designated as the M59.

Carriage M1

The gun carriage provides a stable, yet mobile, base for the gun. The new split-trail carriage featured an eight-wheel integral two-axle bogie and a two-wheel limber that supported the trails for transport. The carriage was a two-piece design. The upper carriage included the side frames with trunnion bearings that supported the recoil mechanism that carried the gun cradle, slide and gun tube. The upper carriage also incorporated the elevating and azimuth gearing. The upper carriage pivoted in azimuth on the lower carriage. The lower carriage included the transport suspension and the split-trail that stabilized and absorbed recoil when the gun was fired.
After the gun was placed in a firing position with the gun pointing in the desired direction, the trails were lowered to the ground and the limber was removed. The carriage wheels would then be raised using built-in ratcheting screw-jacks, lowering the gun carriage to the ground. Once on the ground, the limber-end of the trail legs were separated to form a wide "vee" with its apex at the center of the carriage pivot point. A recoil spade at the limber-end of each trail leg required a correctly positioned hole to be dug for the spade, which was attached to the trail end, to transmit the recoil from gun carriage through the trails and into the earth. This made the gun very stable and assisted its accuracy. The removable spades were transported in brackets on the trail legs.
The carriage M1 and M2 were shared with the 8 inch Howitzer M1, differing only in the gun tube, sleigh, cradle, recoil and equilibrators, weight due to the heavier barrel.
Bottom carriageTop carriage
Firing support baseElevating mechanism
TrailsTraversing mechanism
Retractable suspension systemGun support components
AxleEquilibrator
BrakesCradle
WheelsRecoil mechanism
Sleigh
Gun tube

Specifications

Service

The Long Tom saw combat for the first time in the North African Campaign on December 24, 1942, with "A" Battery of the 36th Field Artillery Battalion. Eventually it equipped about 49 battalions, including 40 in the European Theater and 7 in the Pacific. It was used by several Marine defense battalions, notably during Operation Cartwheel in 1943.
The preferable prime mover was initially the Mack NO 6×6 7½ ton truck; from 1943 on it was supplemented by the tracked M4 High Speed Tractor.
A small number of Long Tom guns were authorised for supply via lend lease channels, to the United Kingdom and France. The authorised establishment of British batteries, including four batteries from the Dominion of Newfoundland, totalled 88 guns.

Variants

Gun variants:
Carriage variants:
Limber variants:
The gun was also mounted on a modified M4 medium tank chassis, in mount M13. The resulting vehicle was initially designated 155 mm Gun Motor Carriage T83 and eventually standardized as 155 mm Gun Motor Carriage M40.
155 mm Gun Motor Carriage T79, based on T23 Medium Tank chassis, never advanced past proposal stage.
A portable "Panama mount" M1 was also provided.

Ammunition

The gun utilized separate loading, bagged charge ammunition. The propelling charge consisted of base and increment. The data in the table below is for supercharge.
TypeModelWeightFillerMuzzle velocityRange
APBC/HEAP M112 ShellExplosive D2746 ft/s 24,075 yds
HEHE M101 ShellTNT2800 ft/s 25,714 yds
SmokeWP M104 ShellWhite phosphorus 2800 ft/s 25,940 yds
SmokeFS M104 ShellSulfur trioxide in chlorosulfonic acid2800 ft/s 25,940 yds
ChemicalH M104 ShellMustard gas, 2800 ft/s 25,940 yds
DummyDummy Mk I Projectile–––
DummyDummy M7 Projectile–––

Existing examples

Pakistan

, Slovenia

Slovenia