In many ways, the M2 Medium Tank was a stepping stone design for American armored warfare leading up to World War 2. The more successful M3 Stuart Light Tank and M3 Grant/Lee and M4 Sherman medium tank series would not have been made possible if not for the previous endeavors that were the M2 Light Tank and the M2 Medium Tank. The M2 Medium Tank, itself, was designed as an enlarged version of the preceding M2 Light Tank design and initially born as the "T5" prototype under the direction of Rock Island Arsenal. In all, 112 of the type were ultimately produced.
The T5 was more than a larger M2 Light Tank - it was given several key features that certainly differentiated the type from the previous offering. An additional road bogie was added to each track side and a new hull superstructure was devised. Like the M2 Light before it, the M2 Medium utilized the same Vertical Volute Suspension System (VVSS) and incorporated much of the same machinery. The superstructure was well formed with sloped sides, particularly along the glacis plate, as well as a 360-degree traversing turret along the hull roof. Machine gun sponsons were added along the hull superstructure sides to help defend the vehicle at multiple angles. The vehicle would rely on a crew of six personnel to man the various controls and guns and included the driver, tank commander, main gunner and several machine gunners. The engine of choice became the Wright R975 air-cooled radial engine. The United States Army adopted the T5 prototype as the "M2 Medium Tank" and a contract was delivered in 1940. In response, Chrysler's newly established Detroit Arsenal Tank Plant took on the procurement contract for 1,000 initial M2 tanks.
Design of the M2 Medium Tank was conventional by 1930 standards. The track sections ran about the sides of the hull with the drive sprocket at the front and the track idler at the rear. Three bogies were affixed to the hull sides, each managing two double-tired wheel assemblies. The hull was multi-faced with some regions well-sloped and others vertical in their design. The glacis plate emerged into a pyramid-type shape at the hull front and provided the compartment for the driver, vision being through three small vision slits. The dual-machine gun sponsons were aft and to either side of the driver's compartment. Entry/exit was through hinged doors on either side of the hull. The turret resided on the hull roof and provided unfettered access to enemies at all attack angles. The engine was fitted to a compartment in the rear of the hull. As a rather novel design feature, "deflector plates" were added over the rear fenders so machine gunners could "ricochet" their bullets downwards and to the rear - this intended to attack enemies as the M2 crossed over an open trench.
Primary armament for the M2 series was the 37mm Gun M3 to which 200 projectiles were carried aboard. One of the more interesting facets of the M2's armament array was its use of no fewer than seven (as many as nine) Browning .30-06 machine guns. One was fitted coaxially in the turret alongside the main gun while pairs were emplaced at either side sponson. A pair was also fitted in fixed, forward-firing mounts at the lower portion of the glacis plate - these controlled by the driver with no elevation/traverse offered. An additional (optional) two machine guns could be affixed externally to the sides of the turret as an anti-aircraft defense measure. In all, there would be 12,200 rounds of .30-06 ammunition carried for the machine guns alone.
By this time, events in Europe - particularly the tank battles that dotted the Axis invasions of various countries - showcased several weaknesses in current accepted American armored doctrine. The M2 was more or less an obsolete addition to the US tank corps as soon as it became available and warplanners needed to review the program to help salvage some of its remaining value. The M2's basic design promoted a very high profile which made it a tempting target to enemy gunners. Additionally, the crew of six operated in rather cramped conditions and the powerplant was somewhat underpowered for the role. The machine gun sponsons were a design quality from a world war gone by and held little value on the modern battlefield. The 37mm main gun armament was also limited in its tactical value when compared to German, French and Soviet tank offerings of the time. The deflector plates were another design feature that served little purpose on the European battle-scape.
After some 18 M2s had cleared the Rock Island assembly line and formally entered evaluations with the US Army, there came a revised specification that created the new "M2A1" standard. This new form brought about additional armor protection and a more powerful Wright R975 EC2 air-cooled radial engine of 400 horsepower. Operational range was 130 miles with a top road speed of 26 miles per hour. The turret was enlarged to a small degree.
As Detroit Arsenal Tank Plant production had now shifted to the more modern M3 Grant/Lee Medium Tank series, the Rock Island Arsenal was given the task of producing the evolved M2A1 variants to which 94 vehicles were completed. Once manufacture of these systems wrapped up, all M2 production ended.
Owing to its obsolete status, the M2 Medium Tank was held in reserve for training new generations of American tankers and were destined to never see combat action. In its place came the M3 Grant/Lee and M4 Sherman - which did much to help win the war for the Allies.