From the opening day of the war until the cessation of hostilities, the Atlantic was a major theatre of operations. Before the Allies could build an army to take back North Africa or the European continent, they had to secure and protect the shipping lanes to England.
At the end of World War I, the Allies decried and outlawed unrestricted submarine warfare at the London Naval Treaty Conference of 1930. Unrestricted submarine warfare was one of the stated causes of American entry into World War I, and the use of submarines was seen as a terror weapon against a civilian population.
At the start of World War II, the Germans had several pocket battleships capable of commerce raiding, converted merchant ships called Q ships for stealthy attacks, and fifty-seven U-boats; only twenty-six were oceangoing U-boats. The early German torpedoes, like the Americans later in the war, suffered from faulty torpedoes that broke up upon impact instead of detonating. Kontradmiral Karl Dönitz had commanded the first U-boat group in 1936, and had risen to command all the U-boats by the start of the war. Unlike the Americans, he quickly moved to fix the torpedo problem. It was not completely fixed until December 1942, well into the war.
Had the Allies known that the Germans were having torpedo problems, they would have been grateful for that small favor. The Germans scored early successes that forced the British to adopt exactly the wrong tactics to fight the U-boats. In September 1939, U-29 sank HMS Courageous, and torpedoes that hit HMS Ark Royal broke up on impact. The Admiralty under Winston Churchill pulled the carriers from antisubmarine patrol and put the merchantmen into convoys. While this allowed mutual assistance among the convoy ships, it also allowed the Germans to focus multiple U-boats on the convoy and vector in subsequent attacks by radio. By October 1, 1939, the Germans had sunk 41 merchant vessels for a total of 153,000 tons displacement. It was a “happy time” for the U-boats. Imagine what havoc the U-boats would have wreaked with fully functional torpedoes.
Even though the number of U-boats on patrol was cut in half in October as ships returned to port to rearm and refuel, more were sunk the next month. U-48 sank HMS Royal Oak inside the supposedly submarine-proof home anchorage in Scapa Flow on October 14, 1939. Throughout the end of 1939, more ships were being sunk then were being built.