Editing U-boat (section)

==Interwar years (1919–1939)==
[[File:Vetehinen-Crichton-Vulcan-1930.jpg|thumb|The Finnish submarine ''Vetehinen'' in 1930 on the slipways at the [[Crichton-Vulcan]] shipyard in [[Turku]], Finland]]

=== 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}}

=== Developments ===
[[File:Bundesarchiv Bild 101II-MW-5536-01, Wilhelmshaven, U-Boot, Torpedo-Übernahme.jpg|thumb|A torpedo is loaded into a U-Boat through a torpedo hatch.]]
Compared to their World War I equivalents, the German U-boat designs of World War II were greatly improved. By using a new steel alloy and by [[welding]] instead of [[rivet]]ing, they had stronger hulls and could dive deeper. The diving time was decreased to thirty seconds for a medium U-boat. The power of diesel engines was increased, so U-boats had a greater surface speed. Range was increased by installing fuel [[Saddle tank (submarine)|saddle tanks]], which were on open to the sea on the bottom in order to balance pressure, with the diesel fuel floating freely on the seawater within the saddle tank. Also, a technique was developed for economical cruising where only one of the two diesel engines would be run and would drive the two propeller shafts through a coupling with the two electro engines.{{Sfn|Blair||pp=|p=37}}

Another vast improvement was the introduction of new torpedo types for the U-boats: the classic [[G7a torpedo]] propelled by compressed air had a much larger warhead than its WWI equivalent, but more important was the introduction of the electric [[G7e torpedo]].{{Sfn|Bekker||p=129}} This torpedo was slower and had less range, but it left no telltale bubble wake and was, hence, ideally suited for daylight attacks.{{Sfn|Blair||pp=|p=37}} During WWI, the Germans had briefly experimented with [[magnetic pistol]]s and these were further developed now as the standard pistol for torpedoes. The classic contact pistol required a torpedo to detonate against the ship's hull, whilst a magnetic torpedo could detonate below a ship, resulting in a much more damaging explosion. Thus, it was hoped that one torpedo would suffice to break the back of a ship, and a U-boat could sink many more ships with its supply of torpedoes.{{Sfn|Blair||p=38}}{{Sfn|Bekker||p=120}}

All U-boats were now also equipped with long- and short-wave transmitters, which enabled them to communicate with bases ashore and with fellow U-boats at sea. This allowed for better operational information and guidance.{{Sfn|Blair||p=38}}

=== U-Boat design and layout ===
[[File:VIIC uboat shaded.svg|thumb|upright=1.8|Cross-section of a Type VII U-boat]]
From bow to stern, A typical U-boat design comprised these sections:

* Bow torpedo room. The torpedo tubes were loaded but torpedoes needed maintenance so there was space to unload the tubes. Below the floor plates four spare torpedoes were stored. Two more spares were stored above the floorplates where they occupied much of the available space. The crew responsible for the torpedo maintenance and launching had their sleeping bunks in this compartment, along with the lowest ratings on board. As long as the two spare torpedoes above the floorplates were not launched, living conditions were very cramped here. Once launched, space for extra bunks became available but, anyway, there were not enough sleeping bunks for all the crew, and these were 'hot bunks' which switched occupants as they went on or off duty.{{Sfn|Blair||p=|pp=57-59}}{{Sfn|Paterson||pp=55-56}}
* Crew quarters for [[officer]]s and [[chief petty officer]]s,{{Sfn|Gannon||p=34}} with a battery compartment below decks.{{Sfn|Blair||p=|pp=57-59}} The captain had a curtained bunk which faced two small rooms: the radio room and the hydrophone room.{{Sfn|Gannon||p=34}}
* Control room. The main large [[periscope]], for general use, was located here. The rudder, [[diving planes]], [[Ballast tank|ballast]] and trim tanks were operated here with valves and buttons. Below decks, there was space to retract the periscope and to store ammunition for the deck gun. A cylindrical tube with a ladder led to the [[conning tower]].{{Sfn|Blair||p=|pp=57-59}}
* Conning tower. This space protruded from the cylindrical hull but was still within the pressure hull. Here, the angle and depth settings for the torpedoes were calculated with an analogue data solver. During submerged attacks the captain was on station here, operating the second, smaller attack periscope, which generated less wake at the surface. Above the conning tower was the bridge.{{Sfn|Blair||p=|pp=57-59}} 
* Aft crew quarters for [[petty officer]]s, with another battery compartment below decks. The galley and toilet were also located here.{{Sfn|Blair||p=|pp=57-59}}
* Engine (diesel) room. The diesel engines needed air, which was supplied through a pipe outside the pressure hull from the bridge, as high as possible from sea level. There was no exhaust pipe; in order to reduce smoke the exhaust was mixed with sea water. The diesel engine could drive an air compressor in order to feed air tanks needed for venting the ballast tanks.{{Sfn|Blair||p=62}}[[File:VII C U-Boot E-Maschine b.jpg|thumb|upright|The electrical room]]
* Electrical or motor room. The electric motors were driven by the batteries. Alternatively, when driven by the diesel engines, the motors acted as generators for recharging the batteries.{{Sfn|Blair||p=62}}
* Aft torpedo room. Only bigger type IX U-boats had such a compartment. Smaller U-boats did not have aft torpedo tubes at all, or had a single torpedo tube installed in the motor room, with a spare torpedo stored below decks between the engines.{{Sfn|Blair||p=62}}