For those expecting a Larry Craig joke, you'll be disappointed. Basically, a secret screw (propeller on a submarine) became unsecret through the use of ... Microsoft's Virtual Earth.
Secret screw? Oh those are nice... Oh, propellers? That one looks very fanny. -as in "like a fan". NOT as in bottoms or front-bottoms :P.
Good on MS! They did something cool for once! Google Earth Fuzzed out all the military bases near me ages ago