155 mm Long Tom The 155mm Gun M1 and M2 ( later M59 ) , widely known as Long Tom , were 155 millimeter caliber field gun s used as a heavy field weapon and is also classed as secondary armament for seacoast defense by the United States armed forces during World War II and Korean War . The Long Tom replaced the Canon de 155mm GPF in United States service . The gun could fire a shell to a maximum range of , with an estimated accuracy life of 1 , 500 rounds . 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 development work began in the United States on a design to improve upon the existing models of heavy gun and carriage . 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 breech that incorporated a vertically - hinged breech plug support . This type of breech used an interrupted - thread breach 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 are packaged , shipped and stored separately . The shell is lifted into position behind the breach 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 . Service . The Long Tom saw combat for the first time in North African Campaign on December 24 , 1942 , with " A " Battery of the 36th Field Artillery Battalion . Eventually it equipped about 49 battalion s , including 40 in the European Theater and 7 in the Pacific . The preferable prime mover was initially the Mack NO 6x6 7½ ton truck ; from 1943 on it was replaced 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 ( 184 ) and France ( 25 ) . However , the authorised establishment of British batteries ( excluding training units ) , 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 ( 9 . 23 kg ) and increment ( 4 . 69 kg ) . The data in the table below is for supercharge ( base and increment ) .