37mm

37 mm refers to a class of firearms and artillery calibers with a bore diameter of 37 millimeters (about 1.46 inches). The designation has been applied to several families of autocannons and anti-tank guns used by various nations, particularly in the interwar period and the early years of World War II. Weapons of this caliber were commonly employed in light anti-tank roles, as anti-aircraft guns, and in some armored vehicles.

In practice, 37 mm weapons offered a balance between rate of fire, recoil, and payload, but their effectiveness declined as armor and aircraft performance improved. Notable examples include the German 3.7 cm Pak 36 light anti-tank gun and the American 37 mm anti-tank gun and related gun mounts used on early-war light tanks and armored cars. Some 37 mm guns also served in anti-aircraft roles and in naval or coastal defense applications. Across different nations, these weapons tended to be surpassed in both firepower and armor-penetration capability by later calibers, leading to their gradual retirement from frontline service after the mid-20th century.

Technical characteristics varied by model but typically included a high-velocity round, a variety of armor-piercing and high-explosive projectiles, and recoil systems suited to lightweight mounts. Penetration and armor compatibility were modest against mid- to late-war armor, which contributed to the shift toward larger-caliber weapons in subsequent decades.

Beyond military use, the 37 mm designation appears in civilian contexts as riot or launch systems that fire 37 mm rounds, including non-lethal or signaling rounds. Today, 37 mm firearms are largely of historical interest or used in training and demonstration roles.