In the 1970s, the Soviet Union developed explosive reactive armor as a way of quickly adding protection to tanks and other heavier armored vehicles. ERA works by, well, exploding. When an incoming ...

Despite the M2’s relatively small size, the tank had a full, four-member crew size which consisted of a gunner, driver and co-driver, as well as a commander who pulled double duty as a loader.

The M2 quickly became obsolete: though adequate for early-war lightly armored Japanese tanks, the 37mm gun was ineffectual against the war’s later, up-armored vehicles.

During the 1930s, tank armor was improved steadily, but remained thin enough to be potentially vulnerable to specialized anti-tank rifles. Most militaries at the time had such a rifle.