The corvette first approaches the U-boat head-on, thinks better of it and swings far around astern of the wreck, then beats upwind towards it. That way, Waterhouse reckons, the wind will tend to blow them away from the reef. Seen from underneath, the U-boat is actually kind of fat-cheeked. The part that’s supposed to be above water, when it’s surfaced, is neutral grey, and it’s as skinny as a knife. The part that’s supposed to be below, when it hasn’t just crashed into a great big rock, is wide and black. She has been boarded by adventuresome Royal Navy men who have cheekily raised a White Ensign from her conning tower.