The German U-Boats very nearly succeeded in winning WW2 for Germany, and the reason they didn’t is a fascinating little story of an exciting sea battle, a fluke, and a fairly substantial violation of the Geneva Convention.
In the build-up before the War, the Germans worked on building up a fleet of submarines, subverting the Versailles treaty by building them and training their crews in Turkey, Spain, and Holland. German Admiral Karl Dönitz devised a highly successful attack strategy (and at the Nuremberg Trials was sentenced to 20 years). Within the first three months of launching their U-boat campaign, the Germans had successfully sunk 114 of Allied merchant ships, losing only 9 of their own.
The Brits were close to losing when the U.S. entered the war.
Allied success in breaking the German Enigma code was an important help early in the war, but changes to the naval Enigma code at the beginning of 1942 stopped the flow of intelligence, bringing an increase in the loss of Allied ships. Furthermore, the U.S. entered the war unprepared and did not initially effectively protect its ships. As a result, a small number of U-boats in the North American and Caribbean coastal waters sank nearly 500 Allied ships in the first half of 1942. (January-July 1942 was the second “Glückliche Zeit” for U-boat crews ). By July 1942, Dönitz had 300 U-boats, with 140 operational at once, hunting in wolf packs and sinking shipping at an annual rate of seven million tons, five times the rate of British replacement capacity. U-boats operated almost unopposed in the “Mid-Atlantic Gap” — the area that could not be reached by aircraft from Canada or Britain — supplied by special vessels known as “milch cow”‘ carrying additional torpedoes and food. German naval intelligence broke British codes and directed submarines to intercept convoys.
U-boat sailors had a life expectancy of about 3 months at sea, as the German command had every expectation that the captain of the submarine would scuttle it rather than permit it to be captured, and often the submarines were scuttled with the men still on board.
In June of 1944 the American Navy succeeded in capturing a U-Boat for the first time. In fact, U-505 was the first warship captured at sea by the US Navy since 1815, when USS Peacock seized HMS Nautilus during the War of 1812. (wikipedia)
On board that u-boat were two enigma machines, which changed the course of the war:
After the capture, the Enigma machines and the 900 pounds of codebooks and publications removed from the sub were rushed to U.S. Naval Intelligence in Washington, D.C. to help the Allied code breaking effort. The ingenuity of Allied code breakers, combined with German blunders, made it possible for the Allies to read most messages to and from U-boats from November 1943 until the end of the war.
In order to protect this important secret, that a U-boat had been captured enabling us to break the codes and read most messages, the prisoners captured from the u-boat (around 55, as I recall, and only one German sailor died) in June of 1944 spent the remainder of the war in a prison camp in Louisiana. They were isolated from other prisoners, denied access to Red Cross visits, and all mail was confiscated, and their families presumed them dead. Indeed, by the late summer of 1944 the German Navy told the families they should presume their sailors dead. Their families were not told they were alive until 1945. They were not released until well past the end of the war. They were sent to England to do some work putting up housing for returning British veterans. the last returning home in 1947.
Back in 2007 The Volokh Conspiracy wrote about this in connection with the ethical and legal questions.
He linked to this post, where the discussion in the comments as to what is and is not a war crime is very interesting as well.
You can visit the only German submarine in American if you ever go to Chicago’s Museum of Science and Industry. It’s a fascinating exhibit, and you can read more about it here.
General information about the submarines here.
While in prison camp in Louisiana, the German sailors were guarded by the Navy baseball team, a fascinating story of its own, and the team taught the Germans to play baseball in an attempt to maintain their chances to play professionally after the war. There’s supposed to be a movie about it some time this year, Playing With the Enemy. You can read the book, too.