M1921 (U.S. Ordnance M1921 Medium Tank)
Prototype Medium Tank
The M1921 became an American interwar venture that went nowhere - budget cuts and a lack of interest by the Army dooming the initiative.
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American tank doctrine and its design/development principles were largely influenced by the British lead in the field. As such, the tanks appearing in the immediate decade after World War 1 (1914-1918) had a largely British flavor to it. In 1919, the United States Army began studies into doctrine involving weight-class-based tanks in which each type held a particular role on the battlefield. Light-class forms, lightly armed and armored, could be set aside for scouting duties and infantry support work. Heavy tank types would form the bulk of the armored force charged with tackling enemy positions and armor directly. The medium tank was then envisioned as an exploit machine, breaking through enemy-held lines and attacking along the exposed sides and rear of an enemy position.
The British adopted this doctrine back in World War 1 when it coupled its heavier lozenge-shaped heavy tanks with the nimbler Medium Mk A "Whippet" tanks in overtaking the enemy. From this was born the World War 2 concept of the British "Cruiser" and "Infantry" tanks that spawned many types developed to fulfill the roles. Cruiser tanks were the lighter exploiting vehicles with the infantry tanks charged with plowing through the enemy.
With that, Army engineers began work on an indigenous medium-type tracked combat vehicle which became the "M1921", a one-off 23-ton pilot (prototype) vehicle constructed at the Rock Island Arsenal. The model was used in a developmental sense but, in the long run, was seen as a possible replacement for the aged stock of foreign-born French and British tanks taken on in number during World War 1. Unlike the early British tanks, the Americans went the French route and adopted a turreted main gun armament design. The primary armament became the 57mm anti-tank gun based on the British 6-pounder. Secondary armament was 2 x 0.30 caliber Browning machine guns for infantry defense. Armor protection reached 25mm of riveted steel construction and the operating crew numbered two. Power was served through a Murray & Tregurtha 250 horsepower engine which allowed for speeds of up to 10 miles per hour on ideal surfaces.
The vehicle began evaluation at the Aberdeen Proving Ground in Maryland during 1922 under the designation of "U.S. Ordnance M1921 Medium Tank".
Also in 1922 was the arrival of the "M1922", a slightly evolved design based on the M1921 though utilizing a British-originated suspension system. Additional changes included a raised rear hull superstructure and lengthened hull overall. The effort intended to improve cross-country performance as well as trench-crossing initiatives.
Despite the two endeavors - which held merit in the interwar years - the world's armies were in a massive military drawdown mode which hampered many-a-program thereafter. The U.S. Army's interest in a new and expensive armored vehicle waned into the decade as surplus war products were still readily available and the prospect of another years-long war in Europe was limited. As such, the M1921 and M1922 programs fell to naught.
Before the M1921's history was officially written, Army engineers fitted the chassis with a Packard engine during 1925 - intended to improve the weaker, original gasoline unit with a more purpose-built powerplant. The change produced the developmental "Medium Tank T1". This product, too, was then cancelled and work continued down other possible routes.