American light tank development can be traced back to the 1920s when several infantry-support light tanks were developed in small numbers. By the early 1930s these designs had evolved into the Light Tank M2, and there were a series of designs all using the M2 designation. For its day this series were quite well armed, with a 37-mm (1.46-in) main gun, but by 1940 the type was at best obsolescent and was used only for training after reaching its apogee with the M2A4 model.
The events of 1940 in Europe were followed closely by the US Army, which realized that thicker armour would be required by its light tanks. This involved a better suspension to carry the extra weight and the result was the Light Tank M3, based generally on the M2A4. It was in full-scale production by 1941, and mass production of the M3A1 really got under way once the USA had entered the war. Early versions used riveted construction, but welded turrets and eventually welded hulls were successively introduced, and there were also many detail design changes. By the time M3 production ceased 5,811 had been built. Basic armament of the M3A1 was one 37-mm (1.46-in) gun with a co-axial 7.62-mm (0,3-in) machine-gun, and four other 7.62-mm (0,3-in) machine-guns (one on the turret roof for AA defence, one in the hull front and two fixed in the sponsons for operation by the driver). Armour thickness ranged from 15 mm (0.59 in) to 43mm (1.69 in).
The Light Tank M3 was used wherever the US Army was involved. It proved to be a thoroughly reliable vehicle and was greatly liked by its crews. Large numbers of M3s were passed to the USA's allies, and the largest recipient was the UK, where the M3 was known as the Stuart. To British eyes the Stuart was large for a light tank, but crews soon learned to appreciate the nippiness and reliability of the vehicle. One thing they did not particularly like was the fact that two main types of engine were fitted to different versions: the normal engine was a Continental 7-cylinder radial petrol engine (Stuart I), but in order to expedite production at a time of high demand the Guiberson T-1020 diesel engine was substituted (Stuart II). This sometimes caused logistic supply problems but it was a burden the Allies learned to survive, Major variants were the M3A1 (Stuart III and Stuart IV with petrol and diesel engines) fitted with a gyrostabilized gun, powertraverse turret and turret basket, and the product-improved M3A3 (Stuart V) with a larger driving compartment, thicker armour and no sponson guns.
The 37-mm (1.46-in) gun was retained throughout the production life of the M3. By 1944 it had very little combat value, so many M3s and Stuarts serving with reconnaissance units had the turret removed to assist concealment. Extra machine-guns were carried instead. Many of these turretless M3s were employed as command vehicles by armoured formation commanders but these were not the only variations upon the M3 theme. The M3 was widely used for all manner of experiments that ranged from mineclearing expedients to flame-throwers of several kinds. Some vehicles were used for carrying self-propelled artillery, but none were accepted for service. There was even an anti-aircraft version.
With the Allies the M3/Stuarts were used from the North African campaign onwards, Some were passed to the Red Army under Lend-Lease arrangements. The Light Tank M5 was a development powered by twin Cadillac engines that was otherwise generally similar to the M3 series but was recognizable by the raised rear decking that accommodated the twin engines. In British service the M5 was the Stuart VI, the same designation being used for the M5A1 with an improved turret having a bulged rear for radio (as on the M3A3).
Specification Light Tank M3A1 Crew: 4 Weight: in action 12.927 tonnes Powerplant: one Continental W-9709A 7-cylinder radial petrol engine developing 186.5 kW (250 hp) Dimensions: length 4.54 m (14 ft 10.75 in); width 2.24 m (7 ft 4 in); height 2.30 m (7 ft 6.5 in) Performance: maximum road speed 58 km/h (36 mph); range 112.6 km (70 miles); fording 0.91 m (3 ft); gradient 60 per cent; vertical obstacle 0.61 m (2 ft); trench 1.83 m (6 ft)