Battle of the Atlantic

The Battle of the Atlantic was a six year naval struggle between the Allies, attempting to get supplies to Europe, and the German U-boats, attempting to starve Britain into submission.

Winston Churchill said that it was the only thing that really frightened him during the war.

U-boats

Having faced U-boats during World War I, the British quickly implemented a convoy system at the beginning of the war and enforced a blockade on Germany. They were short of escort ships though, so many merchant ships had to sail without protection.

With the German conquests of Norway and France in 1940, U-boats gained advantages. The French Navy was removed as an Allied force, and additional ports in France on the Atlantic Ocean became available as submarine bases. The Royal Navy became severely stretched, having to remain stationed in the English Channel to protect against a German invasion, send forces to the Mediterranean Sea to make up for the loss of the French fleet, and provide escort for merchant vessels. This was somewhat mitigated by the Destroyers for Bases Agreement with the United States Navy in September 1940, in which the British exchanged several of their overseas bases for fifty destroyers which were then used for escort duties. The success of U-boats in this period led to an increase of their production and the development of wolf pack tactics.

Surface

The German surface navy, which had suffered substantial losses in the capture of Norway, had mixed results. While there were several successful merchant raids, they also suffered several losses. Notably the Graf Spee, a pocket battleship, was tracked down off the coast of South America and forced to scuttle.

The Bismarck, one of the most powerful battleships in the world, broke out into the Atlantic, sinking the HMS Hood along the way. After an extensive chase it was sunk. Following this engagement Hitler forbade further breakout attempts and kept the German surface fleet close in to Norway and the Baltic Sea.

In May 1941, the British captured an intact Enigma machine, which greatly assisted in breaking German codes and allowed for plotting convoy routes which evaded U-boat positions.

Arctic Transports

In the summer of 1941, the Soviet Union entered the war on the side of the Allies, but they quickly lost much of their equipment and manufacturing base in the first few weeks following the German invasion. The Western Allies attempted to remedy this deficiency by sending Arctic convoys to the Russian ports of Archangel and Murmansk. These convoys faced constant harassment from German forces, and shipments had to be suspended for several months at one point.

Later war

In September 1941, many of the U-boats operating in the Atlantic were ordered to the Mediterranean to block British supply routes. When the United States entered the war that December, they did not take precautionary anti-submarine measures; this resulted in shipping losses so great that the Germans referred to it as a second happy time.

In February 1942, several German capital ships that were stationed in the port of Brest, France, managed to comply with Hitler's earlier order and slipped through the English Channel to their home bases in German waters, dealing a significant blow to the Royal Navy's reputation. In June, the Leigh light allowed Allied aircraft to illuminate U-boats that had been detected by the aeroplanes radar, but this was soon negated by the Germans with Metox, a radar detection system that gave them advance notice of such an aircraft's approach. In American waters, the institution of shore blackouts and an interlocking convoy system resulted in a drop in attacks, and the U-boats shifted their operations back to the mid-Atlantic by August.

In December 1942, a strong German surface navy force engaged an Arctic convoy destined for the Soviet Union and failed to destroy a single merchant ship; this resulted in the resignation of Grand Admiral Erich Raeder. He was replaced by Commander of Submarines Karl Donitz, and all naval building priorities turned to the U-boats.

In January 1943, the British developed the H2S radar system, which was undetectable by Metox. As before, this was followed by a counter-invention on the German side, the Naxos radar detector, which allowed German fighters to home in on Allied aircraft utilizing the H2S. In the spring, the Battle of the Atlantic began to turn in favour of the Allies with the pivotal point being Black May, a period where the Allies had fewer ships sunk and the Kriegsmarine lost 25% of their active U-boats. That December, the German surface fleet lost their last active battlecruiser, the Scharnhorst in the Battle of North Cape. By this time, the Kriegsmarine was unable to regain the initiative; Allied production, such as the mass-produced Liberty ships, improved antisubmarine warfare tactics, sea route patrols with long range attack aircraft, and ever-improving technology led to increasing U-boat losses and more supplies getting through. This allowed for the massive supply buildup in the United Kingdom needed for the eventual invasion of Western Europe in mid-1944.