The M3A1 Light Tank was a significant incremental improvement over the earlier M3 Light design program begun originally in 1940.
Focusing on increased crew safety and survivability, the A1 model also incorporated improvements that increased the operational accuracy and lethality of the vehicle when fielded against enemy tanks of equal weight and class. Many of the design improvements incorporated into the M3A1 went on to become international standards for armor design to this day.
Production of the M3A1 began in May of 1942 and continued through February of ’43. Of the nearly 20,000 Stuarts of all classes and types built during the war, production of the M3A1 totaled 4,621 units. Of this number 4,410 were powered by the Continental W-970-9A seven-cylinder, 262 hp, radial gas engine. The balance of this total being powered by the Guiberson T-1020-4 nine cylinder, 250 hp, radial diesel engine. Both these engines utilized a 5-speed syncromesh transmission and the vehicle could attain a top speed on firm ground of 36 to 38 mph. Dimensions for the M3A1 were as follows: Length 173 inches, Width 88 inches and a Height of 100 inches. Total vehicle weight in combat ready condition was 28,500 pounds. Internal fuel storage was a mere 54 US gallons. This gave an affective range without auxiliary external fuel tanks of approximately 70 miles for the gasoline radial and slightly more with the diesel radial. The problem of limited internal fuel storage was to plague the Stuart design throughout its entire service life.
In the inter-war years the tank corps was practically dissolved and research on new armored vehicles languished. What was to become the Stuart series of tanks started with a modest number of design prototypes in the early 1930’s. In some cases the tank builders financed the prototypes themselves in the hopes of selling them to the U.S. Army.
As the level of research began to increase experimental prototypes evolved into one series of tank for the US Army Infantry and a nearly identical series, referred to as the combat car for the US Army Cavalry. At the time the US Congress was of the view that the mechanized tank was intended solely as an infantry support weapon. Leadership within the US Cavalry thought otherwise and so entered into a somewhat surreptitious, parallel design program (a.k.a. the Combat Car) to develop mechanized mobility for the Cavalry as well. Advanced thinkers within the Cavalry such as General John J. “Blackjack” Pershing and then Colonel George S. Patton saw the future need for a totally mechanized cavalry. One that could, when necessary, operate independently of the infantry to bring a fast moving offensive to the enemy.
With changes in the US Congress the two parallel design programs were finally merged into what was to become the M2 Light Tank program. With the development of the M2 the overall appearance of the future M3 and M3A1 designs began to surface. The M2 possessed the now familiar twin pairs of sprung, vertical volute road wheel bogies and the familiar front drive sprocket. Also the M2 possessed the now distinctive almost vertical armored faceplate in front of the driver and the twin vertical front hatches for both driver and bow gunner. These features would set the style for US light armor for a number of years to come. Various M2 designs were fielded, some armed with twin coaxial light weapons in a single turret, others carried larger caliber single weapons and the heaver M2A3 even sported twin turrets on what was a heavier, extended, but still very versatile light tank carriage.
With the coming of the M3 design the vehicle increased in both size and thickness of armor. This larger, heavier vehicle necessitated increasing the amount of track area always in contact with the ground. This increased track contact area would keep overall ground pressure in line with the earlier designs. To this end the fixed rear idler mounted up off the ground as on the M2A3 was replaced with a component from one of the earlier designs, that being, a large trailing idler wheel on a near horizontal sprung arm. This large rear wheel placed a longer run of track in contact with the ground and the spring action of the pivot arm transferred this increased weight to the rear wheel, improving the vehicle’s handling characteristics over rough terrain. To accommodate this spring arm mechanism the twin bogies were moved forward and closer together which also improved overall weight distribution and made for a smoother riding vehicle. Ground pressure for the M3A1 was a mere 10.5 pounds per square inch.