75mm Pack Howitzer M1
The 75mm Pack Howitzer M1 was developed for by the United States Army after World War I to fill a need for a light artillery piece that could be moved across difficult terrain. The gun and carriage were designed to be broken down into several pieces for ease of transport and carriage by pack animals. The 75mm M1 saw combat in Second World War with the US Army, US Marine Corps, and was also supplied to foreign forces.
The 75mm M1 could also be mounted on a non-dismantling carriage to serve as a light field piece. While the ordnance was used as a basis to produce a number of howitzers for self propelled artillery, the 75mm M2 and M3 were used in the 75mm HMC M8 and some LVT models in preparation for storming the Atlantic Wall. In addition, the M1 in its original form was fitted to a number of other self-propelled carriages, though only one of those - 75mm HMC T30 - reached mass production.
Development and production
The Howitzer, Pack, 75mm M1 on Carriage M1 was standardized in August 1927, however production was slow due to slight demand and limited funding. Mass production of the 75mm M1 with slight modifications as the M1A1commenced in September 1940, by which time only 91 M1’s had been built. Production continued spasmodically into 1945, seeing a total of 5, 376 Pack Howitzers and 504 Light Howitzers completed. The principal changes introduced over this production cycle were to the carriage. Carriage M8 saw the wooden ‘pack’ wheels replaced with pneumatic tires on the original box trail platform, while the M3A1 / M3A2 / M3A3 saw the ordnance placed on a new split trail carriage for Cavalry use. The M3 family saw only limited production as the Cavalry abandoned the Light Howitzer concept for self propelled artillery and the M1/M8 box trail group represented the bulk of production.
The Howitzer M1 and M1A1 consisted of tube and breech which were joined together by interrupted threads, for rapid assembly and disassembly requiring only 1/8th of a turn to join or separate. The 20 caliber tube was rifled with a uniform twist of 1:20 tube, while the horizontal sliding block breech was of the manual type. Recoil was handled by a conventional hydropneumatic system with both buffer and recuperator located under the barrel.
The box trail carriage M1 could be dismantled into six mule loads along with the Howitzer M1, weighing between 160lb and 235lb each, comprising of:
• Breech and wheels
• Top sleigh and cradle
• Bottom sleigh and recoil mechanism
• Front trail
• Rear trail and axle.
The M8 Carriage was identical other than its stub axles and pneumatic tired wheels, which being heavier that the wooden artillery wheels of the M1 created an extra mule load for a total of seven. The M8 could also be parceled into nine parachute loads which included 18 rounds of ammunition, or in assembled form be towed by ¼ ton Jeep.
The split trail field howitzer carriages of the M3 family were not dismountable for pack loading, the intention being that they would always be towed on their pneumatic tires. The change to a split trail carriage was partly to greater stability for more accurate fire, and partly to provide a wider arc of traverse in its secondary role as an anti-tank weapon. To further this, the M3 carriages also incorporated a firing platform slung under the carriage between the wheels. When bought to into action this platform could be lowered to the ground, lifting the wheels and providing three point support.
Organization and service
Issue of 75mm Howitzers to the US Army varied somewhat over the course of the Second World War. While it naturally remained the mainstay of artillery support for Mountain units, it also served in support of the Cavalry although being replaced before US troops deployed to Russia, and then in support of the Airborne forces for a time. The US Navy and Marine Corp adopted the M1/M8 as their standard Landing Gun on Cruisers and Battleships, in addition the Marines were to take M8’s ashore for dealing with beach defenses at close quarters and received a number on M3 Carriages for use on Landing Craft for suppression firing over the bows of light landing craft.
By mid war ToE’s a US Army Mountain Division was provided with two 12 gun Battalions of 75mm Howitzers, an Airborne Division was originally allocated two 12 gun Glider Battalions and a Parachute Battalion, while a USMC Division included four 12 gun Battalions.
The introduction of the 105mm M3 Howitzer, which combined a cut down 105mm M2 Howitzer with the 75mm M3 carriage. Saw the 75mm lose much of its wider application as a light howitzer, retreating back to its original niche role as a pack gun in mountain and parachute units.
The principal user of the 75mm M1 Howitzer though most of WWII was actually the Russian Army. In addition to its traditional role as a mountain gun, the Russians employed it as ski-artillery, and supplied it to Partisan units. The Canadian Army maintained two batteries on the Kola Front and a limited number were supplied to India for use in Afghanistan and other Commonwealth forces in the Middle East.
o M1920, M1922A, M1922B, M1923B, M1923E1, M1923E2 - prototypes
o M1 - the first standardized variant. Based on M1923E2 with minor changes
o M1A1 - variant with modified breech block and breech ring.
o M2 - vehicle mounted variant. Tube and breech from M1A1 were used. In order to provide a cylindrical recoil surface, the tube was fitted with an external sleeve. 197 built
o M3 - vehicle mounted variant; like M2 but with recoil surface as a part of the tube. The M2 and M3 barrels were interchangeable
o M116 - post-war designation of the complete weapon.
o M1 - dismantling box trail carriage with wooden wheels
o M2A1, T2, T2E1, T2E2, T2E3 - experimental carriages.
o M3A1 - split-trail carriage with firing base and pneumatic tires.
o M3A2 - M3A1 with shield added
o M3A3 - M3A2 with different wheels and combat tires.
o M8 - M1 with new wheels with pneumatic tires