Slate's Jesse Sheidlower wonders where the expression "balls to the wall" comes from and finds its origins less genital and more militaristic:
Somewhat disappointingly, it has nothing to do with hammers, nails, and a particularly gruesome way of treating an enemy. The expression comes from the world of military aviation. In many planes, control sticks are topped with a ball-shaped grip. One such control is the throttle—to get maximum power you push it all the way forward, to the front of the cockpit, or firewall (so-called because it prevents an engine fire from reaching the rest of the plane). Another control is the joystick—pushing it forward sends a plane into a dive. So, literally pushing the balls to the (fire)wall would put a plane into a maximum-speed dive, and figuratively going balls to the wall is doing something all-out, with maximum effort. The phrase is essentially the aeronautical equivalent of the automotive "pedal to the metal."Link. So you see, it comes from bomber and fighter pilots, and those guys never have dirty minds.
Indexed by tags military, aviation, etymology, balls to the wall.
Image credits: "P-47D Thunderbolt 1-72 Plastic Model Kit by Revell Germany," courtesy Megahobby.com, borrowed for news-reporting and comment purposes.