TWENTY-MILLIMETER MACHINE GUN

a machine gun firing projectiles twenty millimeters in diameter. Note: In the next sentence, LRH jokingly refers to the fact that you can't get the muzzle depressed enough. This is in reference to the fact that a 20-millimeter machine gun is a large weapon and is usually mounted in aircraft or an antiaircraft carriage. To depress the muzzle of a weapon is to press or push it down, to lower it. —Academy Level I Glossary - Approved November 1990

a machine gun firing projectiles twenty millimeters in diameter. Note In the next sentence, LRH jokingly refers to the fact that you can't get the muzzle depressed enough. This is in reference to the fact that a 20-millimeter machine gun is a large weapon and is usually mounted in aircraft or an antiaircraft carriage. To depress the muzzle of a weapon is to press or push it down, to lower it.