As a Second World War freak, for me U has to be for U-Boats, those menacing destroyers of Allied shipping which Hitler used so effectively in the first part of the war. Most historians agree that all through 1939 to 1942 the U-Boats were feared for their sudden attacks as Allied convoys ran the risk of running into packs of U-Boats in the Atlantic waters. It was only after 1943, when Allied bombing severely damaged U-boat pens in Europe and brought the production of U-Boats down from a flood to a stutter that things began to change. Convoys became safer at sea and Allied Navies grew as the strength of the German Kriegsmarine waned. The Battle of the Atlantic raged on and was finally won by the Allies but at great cost: the Allies lost 3,500 merchant ships and 175 warships were sunk for the loss of 783 U-boats.