Locked and loaded is a military slang expression meaning “ready to go”.
It refers to the bullet getting loaded and locked before firing and is alternatively used as a command; lock and load.
The phrase first appeared as referring to flintlock arms that are ready to shoot, as “well locked and loaded”.
It started showing up as “load and lock” in military jargon during the 19th century.
“Locked and loaded” was spread into the speech of everyday people after John Wayne’s 1949 film, Sands of Iwo Jima.
The expression was then adopted by several movies, books as well as video games, further popularizing the phrase.