16 - Submarine Warfare

The Armistice terms of 1918 required Germany to surrender all its U-boats, and the Treaty of Versailles forbade it to possess them in the future. In 1935, however, Adolf Hitler’s Germany repudiated the treaty and forcefully negotiated the right to build U-boats. Britain was ill-prepared in 1939 for a resumption of unrestricted submarine warfare, and during the early months of World War II the U-boats, which at that time numbered only 57, again achieved great successes. 

The first phase, during which the U-boats generally operated singly, ended in March 1941, by which time many merchant ships were sailing in convoy, trained escort groups were becoming available, and aircraft were proving their effectiveness as anti-U-boat weapons. In the next phase the Germans, having acquired air and U-boat bases in Norway and western France, were able to reach much farther out into the Atlantic, and their U-boats began to operate in groups (called wolf packs by the British). One U-boat would shadow a convoy and summon others by radio, and then the group would attack, generally on the surface at night. These tactics succeeded until radar came to the aid of the escorts and until convoys could be given continuous sea and air escort all the way across the Atlantic in both directions. 

In March 1943, as in April 1917, the Germans nearly succeeded in cutting Britain’s Atlantic lifeline, but by May escort carriers and very-long-range reconnaissance bombers became available. After the U-boats lost 41 of their number during that month, they withdrew temporarily from the Atlantic.

Despite the initial faults of America's submarine force, there was optimism. For example, between 1941 and 1945, U.S. Navy codebreakers deciphered Japanese sailing dates, courses, speeds, and routes of naval convoys and formations, unbeknownst to the Japanese. This information was supplied to the U.S. submarine force, which would lie silently in wait for unsuspecting ships. 

Increased submarine proficiency, founded on an all-volunteer service (submariners made fifty percent extra pay), new long-range fleet type models, and the successes of the U.S. Navy codebreakers, by August 1944, found the "Silent Service" inflicting prohibitive losses on the Emperor's merchant marine, scoring key successes against Japanese warships that insured victory in the Battle of the Philippine Sea, and a blockade of the home islands that was strangling the Japanese economy.

Postwar records compiled by the Joint Army-Navy Assessment Committee indicate Japan lost 686 warships of 500 gross tons (GRT) or larger, 2,346 merchantmen, and a total of 10.5 million GRT to submarines during 1,600 war patrols. Only 1.6 percent of the total U.S. naval manpower was responsible for America's success on its Pacific high seas; more than half of the tonnage sunk was credited to U.S. submarines. The tremendous accomplishments of American submarines were achieved at the expense of 52 subs with 374 officers and 3,131 enlisted volunteers lost during combat against Japan; Japan lost 128 submarines during the Second World War in Pacific waters. American casualty counts represent 16 percent of the U.S. operational submarine officer corps and 13 percent of its enlisted force.