The M21 is a circular United States anti-tank landmine that uses a Misznay Schardin effect warhead. The mine uses an M607 pressure fuse, which can be adapted as a tilt rod fuze. The mine is triggered either by pressure, or by the tilt rod being forced beyond 20 degrees from the vertical by a force of more than 1.7 kg, either of these actions results in pressure being transferred via a bearing cap to a Belleville spring, which inverts, driving the firing pin into the M46 detonator. The M46 charge first ignites a black powder charge, which blows off the mine's cover, and clears any earth or debris that may have been on top of the mine. A fraction of a second later the main warhead detonates, driving and compressing a steel plate upwards, with enough force to penetrate 76 mm of armour at a distance of 530 mm. Approximately 200,000 M21 mines were produced in the U.S. and licensed copies, the K441 and K442, were produced in South Korea.