from Wiktionary, Creative Commons Attribution/Share-Alike License
- interj. A command to prepare a weapon for battle.
- interj. Prepare for an imminent event.
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. (Wiktionary)