Balls-to-the-wall

Usually used as an adjectival phrase as in a balls-to-the-wall effort meaning an all-out, maximum effort. The expression is first cited in the military communications during the 1960s in Vietnam (although Korean War veterans claim earlier usage) and the balls here are thought to refer to testicles but some suggest the ball on the top of the joystick of certain military aircraft, which when pushed to the wall or towards the instrument panel denotes maximum speed. It has no etymological connection with backs to the wall.