The M21 anti-tank mine was developed in the United States in the late 1950s and entered service in the early 1960s as part of the Cold War era's engineering munitions upgrade program. Approximately 200,000 of these mines were produced during serial production, demonstrating their importance in the engineering weapons system of the United States and its allies.
It is intended primarily for installation on tank-hazardous routes, roads and approaches to defensive positions where the movement of tracked or wheeled military equipment is expected.