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.
The U-Boat was not a novelty in the Second World War. They had been used in the First World War as well but not on such a large-scale and with such devastating results. Remember it was when the Cunard liner RMS Lusitania was torpedoed in 1915 that public anger influenced the entry of the United States into this war.
There were many stories of daring on the part of the U-Boat commanders which lived on. Gunther Prien’s sinking of the battleship HMS Royal Oak when commanding U-47 in the heavily defended Scapa Flow was one such story.
I found this site Uboat.net to be a veritable storehouse of information about U-boats, and their commanders. You will find here a host of detail about their successes and failures. It was a tough life for the submariners because for long periods of time the U-boats remained submerged under the water. They were pretty cramped and the crew usually had tough routines to look out for enemy targets as also enemy predators like destroyers or mines laid by them. The story of the U-boat is the story of a very different facet of the war which was fought on the land, in the air, and on the sea and in the case of U-boats often under the seas.