The M3/M5 family were the most widespread light tanks in US service during World War II. The M3 was an immediate development of the M2, with thicker armor protection and an improved engine. Early units featured a riveted hull and turret, but were later redesigned with a welded construction. Suspension consisted of vertical volute springs which was common among most US wartime tanks and gave it good ground-crossing ability, which was complemented by its superb speed. By light tank standards, the M3 featured excellent armor protection which benefitted from more prominent sloping in the M5. However this was still insufficient to safely engage most medium or heavy tanks during the second half of the war. Armament consisted of a 37-mm M5 or M6 gun (derived from the towed M3 anti-tank gun) which was adequate for a light tank by mid-war standards though packing less of a punch than the British 2-pdr. Early versions could also carry up to three Browning guns. The M3 was first used by the British in North Africa where it was known as the Stuart, as and affectionately nicknamed "Honey" by its crews which mostly used it in the reconnaissance role. It was also extensively used in Burma by Commonwealth forces, as well as in the Pacific by the US and Allies where it compared favorably with most Japanese light tanks. Despite the introduction of the upgraded M5, it was gradually (but not entirely) replaced by the far more capable M24 in Europe during the final months of the war. M3 and M5s were exported widely after the war, where it was adopted by numerous Asian and Latin American armies, seeing action in the Chinese civil war among other conflicts.

The Light Tank M3 was the result of the standardization of numerous upgrades to the M2A4 and in its basic version, and included a bolted hull and and octagonal turret. It was followed by the M3A1 featuring a revised, rounder turret with power traverse, a gyrostabilizer, and all-welded construction. A major redesign resulted in the M3A3 with numerous structural improvements, most notably a sloped hull and a completely redesigned turret. This was the last variant of the M3 by which time the M5 had entered production. This had some of the same modifications of the M3A3 but with the same turret of the M3A1, and twin Cadillac engines mounted on a raised engine deck. The M5A1 was the most widely produced version and featured the turret of the M3A3. British units corresponded as the Stuart Mk. I (M3), Stuart Mk. II (M3 with Guiberson diesel engines), Stuart Mk. III (M3A1), Stuart Mk. V (M3A3), and Stuart Mk. VI (both M5 and M5A1). The other main combat variant was the M8 Howitzer Motor Carriage armed with a 75-mm M2 or M3 gun in a modified open-top turret. Additionally, some vehicles were modified to carry flamethrowers for the USMC.