The
40 mm grenade is a military
grenade caliber for
grenade launchers in service with many armed forces. There are two main types in service: the
40×46mm, which is a low-velocity round used in hand-held grenade launchers; and the high-velocity
40×53mm, used in mounted and crew-served weapons. The cartridges are not interchangeable. Both 40 mm cartridges use what the US Army during the Vietnam War called the
High-Low Propulsion System.