Since the lifelines to Britain were being threatened by German U boats, there was a need to create convoys that would protect merchant ships. Germany tried to shut Britain down through closing their Atlantic shipping routes. On May 15th 1940 the German submarine U37 went back to the Atlantic to sink British ships. In just two weeks it sank 11 merchant ships. Since it was the first U boat to go back to the Atlantic, it made a good impression and two U boat flotillas were sent to sink merchant ships. At this time the U boat construction program was delivering 13 per month. The capture of France gave materials to boost production, and bases for the U boats were made along the French coast including Kerneval.
Condors were planes that could strike almost as far as Iceland. Secret raiders set sail in the southern Atlantic.The new French bases made attack and dispatch of U boats more efficient because it was closer. British forces were diverted to defend Britain in fear of an invasion rather than protecting the merchant ships, this meant that the merchant ships were left defenceless. Merchant ships were therefore given armor and sometimes arms and a trained crew to fight. In June 1940, nearly half the Royal Navy’s 80 destroyers were sent to protect against an invasion. Britain was only able to protect merchant ships that were less than 100 miles west of Ireland, this meant the these ships were left vulnerable past that point.
Fast convoys coded HX went to Halifax, the slow convoys coded SC went to Sidney. At this time the Royal Canadian Navy had less than 10 destroyers, which could provide the convoy light protection for 400 miles East of the coast and inward. The US remained neutral at this time, however they wanted to keep conflict out of their waters and could protect their coast against long range U boats. As a result the Canadian merchant boats had a huge gap in the middle of the Atlantic with no protection. In late May 1940, U boats went out to the Atlantic to attack merchant ships, however they were hard to find due to the vast size of the Atlantic. However the U boats were equipped with good radio direction finders which pinpointed radio transmits of merchant ships and hydrophones which relied on propellor noises in closer range. Above all, U boats used intelligence such as decoded radio transmissions and German spies hidden in British naval bases. The U boats were told about British departures. In June alone 64 merchant ships were sunk by U boats.They were very successful under the command of Karl Dönitz. Vessels sailing out of convoy were the ones that were most at risk. However boats in a convey were able to deter U boats.
A typical convoy would have the most valuable cargo in the middle. They used a compact rectangle formation because it reduced visibility, left nobody left vulnerable from attacks from the rear. However with more U boats later in the war, Donitz was able to develop tactics that went against the convoys. His idea which worked was to approach the convoy very near to the surface to avoid being detected by radar and sonar. This tactic known as the “wolfpack” was very useful because the U Boats were able to attack the convoy from the sides using their torpedos. The bravest of the U boats would wait for night and steer right into the convoy to attack the more valuable cargo that was defended in the middle of the convoy.
Early september 1940 was when the Kriegsmarine first formed wolfpacks with U boats. Within the first month they sank 59 allied ships. Convoy SC7 contained 34 merchant ships, in October, the Germans were able to find out where this convoy would be because the were able to decode British radio transmissions. Since they has this information, the U boats were able to sink 16 of these ships. As a result of the U Boats being so successful from June to October 1940, the British were 6 million tons of imports short of what was required to win. However, in November, storms forced the U Boats away from attack.
The allied ships were also doing better by strategically heading further north towards Iceland, and merchant radio codes had changed so that the Germans no longer knew what they were doing. At this time, bad weather had also forced Hitler to decide not to invade England. Another benefit for England was that many of the US destroyers were able to defend convoys in exchange for British bases. With this added strength, the U boats were no longer as successful. However the British were still declining in imports because they the Germans had released battleships and aircraft that could sink ships.
The allies were facing many problems, but they were able to capture a German patrol boat; this boat contained code books, and the British were able to locate many of the U boats as a result. With this information convoys were simply diverted away from the enemies. In May of 1941, the Royal Canadian Navy received 8 destroyers and 20 corvettes; along with other new defenses from allies, the convoys were significantly stronger. As a result Donitz decided to transfer the U boats further south to where there was less allied force. With growth in defensive power, Britain was able to keep many of the German surface fleet stuck in Kiel, and unable to leave to the Atlantic. Another win for the British was when they sunk Bismarck, this ship was one of the most powerful German warships and never even saw the convoys it was intended to sink.
In the late spring of 1941, the allies had successful destroyed the bulk of the German surface navy. Even with strengthened convoy defense, the allies were still losing lots of merchant ships. In mid 1941, 8 U boats were sent to the Arctic ocean to destroy merchant ships that were going to Russia, this was a terrible move for Hitler because the war against the Soviet Union significantly increased Britain's ability to import. This distraction that diverted German force to the Arctic enabled Britain to further defend their convoys by providing better air support and faster convoy routes. In June 1941 Americans decided that they would escort convoys that contained non American merchant ships halfway across the Atlantic. In September the Germans transferred U boat wolfpacks back into the gap where merchant ships were still undefended, however in October, Hitler once again demanded these U boats elsewhere. 16 U boats were sent to North Africa, and the allies once again were strong enough to cross the Atlantic and provide the British with plenty of imports.
On December 7th 1941 another important event occurred in this ongoing battle. The attack on Pearl Harbour was made on the US, which resulted in the US being at war with Germany and Japan. Since Germany was now at war they were able to make attack on American vessels in US waters. Operation Paukenschlag was the German opening offensive on the US. It involved 9 type 9 long range submarines. On January 12th 1942 the submarines were station all along the East coast.The first vessel to be attacked was British tanker; within 4 weeks, 50 merchants ships were sunk. More U boats were then transferred to America and the East coast of North America. In February, 55 merchant ships were sunk, which resulted in Britain sending defensive support. City blackouts were ordered by the US federal government so that merchant ships weren’t as easily seen by surfaced U boats. By about August, what was known as the Germans “second happy time” was over due to the overall strengthened defence.
The “second happy time” also diverted the U boats away from Britain, which meant that merchant ships were being attacked less. Admiral Donitz decided to return the U boats to the Eastern Atlantic to reform the wolfpacks, this was a problem for Britain because much of their defence was sent to the US. In 1942 the Hedgehog was developed, it was a anti submarine weapon that essentially fired bombs that would explode upon the impact of a submarine; the hedgehog was a successful weapon for defending against U boats at close range. Escort aircraft carriers were also starting to be used in 1942 by the allies, these carriers not only could be used to spot U boats, they were also used to attack them. However technology kept advancing and U boats were often able to avoid being attacked by a convoy because they had developed meteox radar detector which told them when they had been detected by radar.
In the fall of 1942 there remained a gap in the atlantic that was undefended, this was known to the allies as the “Black Pit”. It was in the “Black Pit that Donitz concentrated his U boats. In November of 1942, SC107, a large convoy was attacked in this area, 15 allied vessels were sunk in just four days.
In efforts to stop the U Boats after a bad year in 1942, the allies needed to make the U boats travel underwater to consume more fuel. With spot lights equipped on planes the U boats were being forced to travel underwater. However the U boats were equipped with a counter measure; they were able to attack planes when they were surfaced with guns. In early 1943 bad weather once again stopped many of the wolfpacks, and once again the convoys were doing well.
In March of 1943, Donitz sent all of his availible U Boats to sea where the “Black Pit” was. Convoys were once again very vulnerable. To add to this, the German gained intelligence of the location of two Convoys (SC122 and HX229) ; one of which contained crucial war supplies from the US. On March 12th, Donitz sent 3 convoys which in total contained 38 U boats at these two convoys. Fortunately that day both convoys managed to sneak past, but on March 16th one of the U boats heading back for repairs spotted convoy HX229. The U boat radioed back to headquarters and all of the 38 submarines were sent to attack HX229. The U boats managed to sink 21 ships from that convoy, which made it the most destructive convoy battle of the war. Although this made it seem like the convoy system wasn’t working, the allies were doing well in another area. Decoding German codes had become more simple, it took just ten day to break the new phyfer. As a result the allies were able to simply route their convoys around the wolfpacks. Another huge gain was the increase in long range air support, which finally made it possible to secure the “Black Pit” or the mid Atlantic gap. All of this combined, secured the North Atlantic.
By stopping the U boats from travelling on the surface, all of the wolfpacks were defeated. Once they had defeated the U boat’s offence the allies went out to attack and destroy all of the remaining U boats. The allies used air attacks to destroy bases where U boats were being made and stored. By April of 1943 the allies had for the first time destroyed more U boats than the U boats had destroyed merchant ships. On May 24th 1943 Admiral Donitz withdrew the surviving U boats from the Atlantic and the battle was over. "Battle of the Atlantic." HISTORY. N.p., 01 Apr. 2014. Web. 10 Jan. 2015. <http://www.history.co.uk/study-topics/history-of-ww2/battle-of-the-atlantic>.