M101 howitzer
Development and designation
### Development and designation

After World War I, the U.S. Army Ordnance Department studied various captured German 105 mm\-caliber howitzers and developed the 105 mm Howitzer M1920 by using the Carriage M1920\. A box trail carriage design (the M1925E carriage) and two other split trail designs (the T1 and T2\) were also developed, but the original split trail design was found superior after testing. After being selected, the piece was standardized in December 1927, as the 105 mm howitzer M1 on carriage M1\. The Army had an intention to replace all [75 mm gun\-howitzers](/wiki/Canon_de_75_mod%C3%A8le_1897 "Canon de 75 modèle 1897") in its divisional and non\-divisional field artillery regiments with 105 mm pieces, but a lack of appropriations stalled the idea and eventually forced it to be completely abandoned by 1929; a limited plan developed in 1925 envisioned re\-equipping three regiments, but by 1933, only 14 M1 howitzers had been manufactured.

A modified version of the M1 was trialed in 1932 which used semi\-fixed ammunition instead of separate\-loading ammunition. Since this development required a different breech block, the new piece was designated the 105 mm howitzer M2 on carriage M1\. 48 pieces were manufactured in 1939\. The original M1 carriage had been designed for towing using horses rather than trucks, and a new carriage, the T5 (M2\), was developed in 1939 and standardized in February 1940\. The breech ring of the howitzer M2 was modified in March 1940 before large\-scale production began, creating the 105 mm howitzer M2A1 on carriage M2\.

In 1939, the new howitzer cost $25,000, which was three times more than a [75 mm field gun M1897 on M2 carriage](/wiki/75_mm_field_gun_M1897_on_M2_carriage "75 mm field gun M1897 on M2 carriage"), and its adoption required procurement of a colossal amount of new ammunition (War Department estimate of $26 million).

The gun was designed to be very durable and was therefore heavy for its caliber,Bishop, Chris. The encyclopedia of weapons of world War II. Sterling Publishing Company, Inc., 2002, p.139 but studies after 1943 found that after prolonged firing, the muzzle end of the barrel was prone to cracking. To relieve stress in the barrel, new production M2A1 tubes were counterbored two inches from the muzzle starting in the late 1940s. By the end of World War II, 8,536 105 mm towed howitzers had been built and post\-war production continued at Rock Island Arsenal until 1953, by which time 10,202 had been built.

In 1953, the new howitzer M2A2 was standardized to further increase the life of the howitzer at the cost of some muzzle velocity. The M2A2's barrel had a higher strength breech ring, deeper rifling grooves, and shallower rifling taper than the M2A1's barrel, resulting in a 50 percent more effective full charge barrel life than the M2A1\.

A further developed howitzer M2A2E2, featuring a muzzle brake and maximal range increased along with the propelling charge, on carriage M2A2E2, featuring an increased maximal angle of fire, were designed and tested in 1958, but with the coming [XM102 howitzer](/wiki/M102_howitzer "M102 howitzer") both were canceled in 1961\.

In November 1960, U.S. military artillery designation system began to change, where howitzer M2A1 or M2A2 on carriage M2A1 were renamed the M101 and howitzer M2A1 or M2A2 on carriage M2A2 were renamed the M101A1\. This howitzer continued to see service through the [Vietnam War](/wiki/Vietnam_War "Vietnam War"). Though the successor M102 howitzer was adopted in 1964, both M101 and M102 shared similar roles in battle and the M101A1 was never fully replaced in front\-line service until the adoption of the [M119 howitzer](/wiki/M119_howitzer "M119 howitzer"). Today, the M101A1 has been retired by the U.S. military, though it continues to see service with many other countries.


Why was the M1 carriage designed for horse towing?