German U-boats Threaten Allied Shipping:
December 1941--June 1942

Before the United States entered World War II, the German submarine offensive against shipping across the North Atlantic was throttling Great Britain. U-boats were sinking merchant ships and tankers delivering war materiel from the United States faster than the British could replace them. The concern for both nations was that German submarines might counterbalance the advantage in resources that the United States provided to Great Britain under the Lend-Lease Act. In the long term, German control of the sea lanes might pose an even greater threat. Early in 1941, British and American leaders held secret meetings in Washington, D.C., to consider the possibility of becoming allies in a war against the European Axis (Germany and Italy) and Japan. The officials that an Allied war in Europe would eventually entail an invasion of Europe across the English Channel. Without American and British control of the shipping lanes, that invasion would be impossible.

Meanwhile, enemy submarine forces concentrated on a single strategic objective: to sink enough Allied shipping to cripple war effort. At the beginning of the war, Germany withdrew its U-boats from operational areas when Allied antisubmarine warfare severely limited their operations against shipping. But German dictator Adolf Hitler saw the Atlantic Ocean as his first line of defense in the west. Nazi U-boats could prevent the Allies from striking back with air and sea power, and from transporting troops and supplies to be used in any land invasion of Europe. When the United States formally declared war on Germany and Italy on December 11, 1941, Germany energetically pursued its submarine strategy.  

The United States was grossly unprepared for an antisubmarine war. The U.S. Navy, under the command of Adm Ernest J. King, was responsible for antisubmarine defenses, but it lacked trained manpower, specialized surface vessels, and long-range (400- to 600-mile radius) or very-long -range (up to 1,000-mile radius) aircraft. Thus, King had to call for support from the U.S. Army Air Forces (AAF) commander, Gen. Henry H. Arnold. But, like the Navy, the AAF was unprepared for antisubmarine operations. AAF aircraft carried bombs rather than depth charges and  lacked radar or other special submarine detection equipment. No trained personnel were available for the specialized job of detecting and attacking
submarines from the air, and the AAF had no organization dedicated to antisubmarine operations. Perhaps the most serious problem was that the few combat aircraft on hand (approximately 3,000) were in sudden demand for many other important operations.
Germany quickly took advantage of this unpreparedness. Within a month of the U.S. declaration of war, the first German submarine arrived in American waters. Between mid-January 1942 and the end of June, U-boats sank 397 ships--171 off the east coast of the Unites States, 62 in the Gulf of Mexico, and 141 in the Caribbean Sea. Many of these were tankers. In the beginning of March Adm. Karl Dönitz, commander of Germany's submarine fleet, used specially modified U-boats to refuel and resupply operational submarines. These "milch cow" submarines, as he called them, extended a U-boat's patrol of five to six weeks to averages of sixty-two days with one refueling and eighty-one days with a second refueling. This practice vastly expanded each submarine's effectiveness in the American theater.

By June, the U.S. Navy, supported by the AAF, had driven most of the U-boats from the east coast, but enemy submarines continued to wreak havoc on Allied shipping in the Gulf of Mexico and the Caribbean Sea. The Allies lost three million tons of shipping and five thousand men, mostly in American waters, during the first half of 1942. The loss of cargo grievously endangered Great Britain's ability to continue the war.