lock and load
Originated in American English, supposedly as an instructional command to prepare an M1 Garand, the main rifle used during World War II, for battle. the expression was popularized 1949 by John Wayne in the movie The Sands of Iwo Jima. Various similar phrases predate it, including in transposed form as “load and lock”. It is disputed whether the command "lock and load" was ever used by the US military. The term, "lock and load" was used in the US Army as late as 1969 and was also used in Vietnam. Tap of the magazine against the helmet and slip the magazine into the M14/16 release the charging handle.
Anyone who has qualified in marksmanship in the US Marines should be familiar with the term. During rapid fire, the Range Master says, "Ready on the left, ready on the right, aaaall ready on the firing line. With 10 rounds, lock and load. Daaawg targets!"
- (US, slang) A command to prepare a weapon for battle.
- (US, slang) Prepare for an imminent event.