M3 howitzer

The 105 mm Howitzer M3 was a U.S. light howitzer designed for use by airborne troops. The gun utilized the barrel of the 105 mm Howitzer M2, shortened and fitted to a slightly modified split trail carriage of the 75 mm pack howitzer.

The howitzer was used by the U.S. Army during World War II. It was issued to airborne units and the cannon companies of infantry regiments.

Development and production
The process of building airborne forces in 1941 led to a requirement for an air portable 105 mm howitzer. The weapon, initially designated T7, featured a barrel from the 105mm Howitzer M2, shortened by 27 in and combined with a recoil system and carriage of the 75 mm field howitzer. A prototype reached trials at Aberdeen Proving Ground in March 1942.

The howitzer was designed to fire the same ammunition as the longer M2. However, it turned out that shorter barrel resulted in incomplete burning of the propelling charge. The problem could be solved by use of faster burning powder. Otherwise the design was considered acceptable and was standardized as 105 mm Howitzer M3 on Carriage M3. The carriage was soon succeeded by the M3A1, which had trails made from thicker plate. Even stronger tubular trails were designed, but never reached production.

The production started in February 1943 and continued until May 1944; an additional bunch was produced in April–June 1945.

Service
Even though the M3 was not mentioned in the February 1944 Tables of Organization and Equipment (TO&E), shortly before the Normandy Airdrops some airborne divisions received a 105 mm glider field artillery battalion equipped with them as a supplement to their existing three 75 mm howitzer battalions. 1/4 ton jeeps were used as prime movers. The weapon was finally authorized as an option by the December 1944 TO&E and, by 1945, employed by all airborne divisions in the European Theater.

The M3 was also issued to the cannon companies of infantry regiments (six, in three platoons of two). Infantry typically used 1½ ton trucks as the prime mover.

A small number of M3s were supplied via lend lease channels to France (94), United Kingdom (2) and countries of Latin America (18).

Variants
Gun variants:
 * T7, standardized as M3.
 * T10 - variant with elevation improved to 65 degrees.

Carriage variants:
 * M3 - based on M3A1 carriage for the 75 mm field howitzer.
 * M3A1 - had stronger trails, made from 1/8 inch plate instead of 3/32 inch.
 * M3A2 - was fitted with shield.

Self-propelled mounts
There were two proposals for a self-propelled artillery piece armed with the M3. Neither reached mass production.


 * 105 mm Howitzer Motor Carriage T38 - based on the M3 halftrack, never built.
 * 105 mm Howitzer Motor Carriage T82 (M3 in mount M3A1) - based on the Light Tank M5A1 chassis. Two pilots were built. The project was cancelled in June 1945 due to lack of requirement.

Ammunition
The gun fired semi-fixed ammunition, similar to the ammunition of the M2; it used the same projectiles and the same 105 mm Cartridge Case M14, but with different propelling charge. The latter used faster burning powder to avoid incomplete burning; it consisted of a base charge and four increments, forming five charges from 1 (the smallest) to 5 (the largest). In an emergency, gunners were authorized to fire M1 HE rounds prepared for the Howitzer M2, but only with charges from 1 to 3. M1 HE rounds for the M3 could be fired from an M2 with any charge.

HEAT M67 Shell had non-adjustable propelling charge. For blank ammunition, a shorter Cartridge Case M15 with black powder charge was used.