Editing U-boat (section)

=== Construction ===
The [[Treaty of Versailles]] ending World War I signed at the [[Paris Peace Conference, 1919|Paris Peace Conference]] in 1919 limited the surface navy of Germany's new [[Weimar Republic]] to only six [[battleship]]s, six [[cruiser]]s, twelve [[destroyer]]s and twelve [[torpedo boat]]s. The treaty also restricted the independent tonnage of ships and forbade the construction of submarines.{{Sfn|Humble||p=25}} In order to circumvent the restrictions of the treaty, a submarine design office called [[NV Ingenieurskantoor voor Scheepsbouw|Ingenieurskantoor voor Scheepsbouw]] (IVS) was set up in the [[Netherlands]]{{Sfn|Costello & Hughes||p=26}} The IVS was run by Krupp and made it possible to maintain a lead in submarine technology by designing and constructing submarines in Holland for other nations.{{Sfn|Blair||p=24}} The IVS made designs for small 250-ton U-boats, medium 500-ton U-boats and large 750-ton U-boats.{{Sfn|Blair||p=31}}

The IVS constructed three 500-ton medium submarines in Finland between 1927 and 1931, known as the [[Vetehinen-class submarine|Vetehinen-class]]. These ships were the prototypes for the subsequent German [[Type VII submarine|Type VII]] U-boat. In 1933 a small 250-ton submarine, the [[Finnish submarine Vesikko|''Vesikko'']] was built. This submarine was nearly identical to the subsequent German [[Type II submarine|Type II]] U-boat. A fifth very small 100-ton submarine, the [[Finnish submarine Saukko|Saukko]] was built in 1933 as well. In Spain a large 750-ton boat was built between 1929 and 1930. After the Spanish lost interest in the U-boat, they sold it to Turkey where it entered service as [[TCG Gür (1936)|Gür]]. German sailors assisted in the trials for these submarines. These secret programs were exposed in the [[Lohmann Affair]] and as a result the Head of the {{lang|de| [[Reichsmarine]]}} [[Hans Zenker]] had to resign. His successor [[Erich Raeder]] continued the policy of secretly breaching the Versailles treaty. On 15 November 1932, a plan was approved for an expansion of the German navy which included U-boats.{{Sfn|Blair||pp=31-32}}

[[File:U-boot E-1.png|thumb|The Spanish submarine E-1 in Cadiz]][[File:u534.jpg|thumb|[[German submarine U-534|''U-534'']], a type IX U-boat at Birkenhead Docks, Merseyside, England]]In 1935, Britain sought to control the increasingly apparent breaches of the Versailles Treaty and it concluded in 1935 the [[Anglo-German Naval Agreement]]. This ended officially the limitation of the Versailles Treaty and allowed Germany to build ships in a 100:35 tonnage ratio to the British fleet. For submarines the Germans obtained a parity in tonnage, but promised a 45 percent limit unless special circumstances arose.{{Sfn|Costello & Hughes||p=28}} This allowed 24,000 tons for U-boat building. Only one week after the signature of the agreement, the first of six Type II U-boats, {{GS|U-1||2}} was commissioned in the German Navy, which changed name from {{lang|de|Reichsmarine}} (Imperial Navy) to {{lang|de|[[Kriegsmarine]]}} (War Navy).{{Sfn|Blair||pp=34-35}} Within the year, the Germans commissioned a total of 36 U-boats for a total of 12,500 tons:{{Sfn|Blair||p=40}}
* Twenty-four small 250-ton Type II U-boats
* Ten medium 500-ton Type VII U-boats
* Two large 750-ton [[German Type I submarine|Type I]] U-boats, based on the design of the Spanish submarine

[[Karl Dönitz]] was appointed as head of the submarine section of the {{lang|de|Kriegsmarine}}. He believed firmly that in spite of the Anglo-German Naval agreement and Hitler's policy of avoiding conflict with Britain, the next war would be with Britain. Based on these views, he requested that the remaining 11,500&nbsp;tons be used for building twenty-three medium submarines, which were in his opinion the ideal type for the commerce war against British convoys. Raeder however did not share these beliefs and opinions and opted for a more balanced expansion of the submarine fleet:{{Sfn|Blair||p=40}}
* Eight small 250-ton improved type II U-boats
* Seven medium 500-ton U-boats. The type VII was designed with a single rudder and this had two drawbacks: as the rudder was not in the wash of the two propellers, the rudder response was not good. The stern torpedo tube had also to be mounted externally as the rudder obstructed the exit of an internal tube. As a consequence, this tube could not be reloaded. Hence the type VII was upgraded to type VIIB with dual rudders to improve maneuverability and to fit an internal stern tube with a reload.{{Sfn|Paterson|2003|p=x-xi}}
* Eight large 750-ton U-boats. The Type I was found to be unsatisfactory: not only had it the same single rudder maneuverability problems of the type VII, but it also had a very poor diving time. The gravity center of the U-boat was too forward, so when surfaced the Type I had its propellers exposed when pitching. Whilst submerged there were problems with depth keeping and stability as air bubbles in the fuel tanks wobbled back and forth.{{Sfn|Paterson|2003|p=x-xi}} Hence a new [[German Type IX submarine|Type IX]] design for a large U-boat was made

Twenty-one of these twenty-three U-boats were commissioned before the start of World War II. In 1937, Britain announced it would expand its submarine fleet from 52,700 to 70,000&nbsp;tons. Again, Raeder decided that the extra 7,785&nbsp;tons would be divided between medium and large U-boats:{{Sfn|Blair||p=45}}
* Seven medium 500-ton type VIIB U-boats
* Five large 750-ton of the improved type IXB U-boats
[[File:80-G-700007 Battle of the Atlantic. German Submarine U-233 sinking after being rammed by USS Thomas (DE 102).jpg|thumb|A type XB submarine sinking in the Atlantic. On the foredeck the vertical mineshafts are visible.]]
During 1938, Hitler changed his attitude towards Britain. Whilst he still hoped that Britain would not interfere in his foreign policy, it became clear to him that he needed a Navy that could act as a deterrent. Hitler wanted to invoke the escape clause of the naval agreement and to have 70,000&nbsp;tons of submarines. Between May 1938 and January 1939, Raeder ordered 52 more U-boats to be completed by 1942:{{Sfn|Blair||pp=46-47}}

* Twenty-one medium 500-ton type VIIB U-boats
* Eleven large 750-ton type IXB U-boats
* Three very large type XB minelaying U-Boats
* Four huge type XI U-cruisers
In 1939, the ambitious [[Plan Z]] was launched. It called for the construction of a German Navy capable of challenging the Royal Navy. The plan included 249 U-boats for a total of 200,000 tons. But when World War II broke out only months after the plan was announced, only a handful of the planned U-boats ended up being built.{{Sfn|Blair||pp=46-47}}

When World War II started, Germany had 56 U-boats commissioned, of which 46 were operational and only 22 had enough range for Atlantic operations, the other 24 were limited to operations on the [[North Sea]].{{Sfn|Mason||pp=|p=23}}