The phrase "balls to the wall," sounds as if it is a reference to a part of the
male anatomy, which causes some confusion as to what it originally meant. However, the original usage has nothing to do with
anatomy, but came rather from military
aviation.
On an
airplane, the handles controlling the
throttle and the fuel mixture are often topped with ball-shaped grips, referred to by pilots as "
balls." Pushing the balls forward, close to the front wall of the
cockpit results in the highest possible
speed.
This phrase is often thought to have come from
railroad work, but there is no
evidence to support that story. No use of the phrase is known to exist prior to the mid-1960s, and all the early
cites are from
military aviation.