The M2 and M3 Half-Track Car were two of the most important armored vehicles in service with the US Army during World War II, and despite their resemblance were used for different roles. The design of the M2 was based on that of Citröen-Kégresse half-tracks developed in France during the 1920 as well as the M3 scout car, whose forward fuselage was adopted almost identically which allowed for standarization of components. The M2 was primarily designed as a reconnaissance vehicle and prime mover for artillery and supplies. In contrast, the M3 was a dedicated armored personnel carrier, replacing the amunition stowage compartment with a lengthened troop compartment which could carry an entire squad of 12 troops (compared to 9 in the M2 when used as a personnel carrier). The troop compartment also featured a rear door for ease of access. The M2/M3 was lightly armored, capable of defending against small arms, although its open top made it vulnerable to plunging fire or grenades. Defensive armament consisted on a M2 0.50-in machine gun on a pintle mount, with one or two additional guns on the side of the troop compartment (depending on version). Both M2/M3 half-tracks entered service in mid-1941 and first saw action in the Philippines. They were later an integral part of US infantry and armored units, enabling it to achieve full motorization of its combat units. Thousands were also provided as Lend-Lease to US allies including UK, Commonwealth, and Soviet forces. It remained in service during the Korean War but preference for fully tracked APCs meant it was gradually phased out thereafter, though many remained in service for decades in nearly four dozen countries.

Early development of half-track cars began through efforts of US ordinance designers and the White Motor Company with the T7 in 1938, followed by the T14 a year later with a more powerful engine. The definitive M2 was designed in 1940 with the M3 development shortly after, with both entering production together by a combination of auto manufacturers. The M2A1 featured a revised machine gun ring mount and rear door while the M3A1 also included the ring mount along with other mechanical improvements. Both had the ability to carry up to three additional pintle-mounted guns on the troop compartment sides. Export versions of the the M2/M3 were built by International Harvester and were designated M9/M9A1 (M2/M2A1), and M5/M5A1 (M3/M3A1) with only minor modifications. Numerous non-APC versions were also producted, many only in prototype form. Artillery variants included the T12 tank destroyer (later redesignated M3 GMC) which was armed with a 75-mm M1897A4 gun, T19 (105-mm) and T30 (75-mm) self-propelled howitzers, M21 mortar carrier, and T48 tank destroyer armed with an M1 57-mm gun. Anti-aircraft variants armed with M2 machine guns included the twin-mounted M13 and M14, and quad-mounted M16 the latter which saw widespread service (a few prototypes with 40-mm guns were also built). Outside the US, the M3 was also extensively used by the Israeli Army post-war, with numerous domestic artillery, and anti-air variants developed.