Editing Battle of the Atlantic (section)

==Final years (June 1943 – May 1945)==
After the defeat on the North Atlantic convoy lanes, it became clear to Dönitz and Hitler that a new generation of U-boats was urgently needed. There was a programme to develop [[Hellmuth Walter|Walter]] U-boats which achieved high underwater speeds with a revolutionary [[hydrogen peroxide]] [[Air-independent propulsion|air-independent]] [[Hydrogen peroxide#Propellant|propellant]] system, but this faced many technical setbacks and these U-boats would not become available in time. Instead it was decided to modify these designs where the new propulsion system was replaced with much larger battery capacity for a conventional U-boat propulsion system, the {{lang|de|[[Elektroboot]]}} types. Since the design was ready, it was hoped that by mass-producing the U-boat in prefabricated sections, these new [[Type XXI U-boat|Type XXI]] oceangoing and coastal [[Type XXIII U-boat|Type XXIII]] would become operational in mid-1944. In the meantime, as a stopgap measure until these ''Elektroboote'' became available, the existing U-boat designs were gradually equipped with a {{lang|de|[[Submarine snorkel|Schnorchel]]}} (snorkel), which allowed U-boats to run their diesel engines whilst submerged and recharge their batteries.{{Sfn|Blair|1996b|pp=311-314}}
[[File:USS Bogue (CVE-9) at Bermuda, February 1945.jpg|left|thumb|The escort carrier USS ''Bogue'']]
The U-boats left the North Atlantic convoy lanes and shifted their attacks to the [[UG convoys|American-Mediterranean convoys]] in the Central Atlantic. The Allies learned from this move through intelligence and anticipated by ordering three US Navy task Groups centred around the escort carriers [[USS Card|''Card'']], [[USS Bogue|''Bogue'']] and [[USS Santee (CVE-29)|''Santee'']] to the region. These escort carriers protected the convoys, but were not part of its close escort and were allowed to search and destroy U-boats and their supporting U-boat tankers on HF/DF bearings. Only 1 ship was lost, but the escort carriers sank 17 U-boats. After this defeat, Dönitz halted all wolfpack operations in the beginning of August until U-boats could be upgraded with better weapons and measures.{{sfn|Costello|Hughes|1977|pp=289-290}}{{Sfn|Blair|1996b|pp=341-346}} At the same time the British were allowed to access the harbours at the Portuguese Azores Islands and to operate Allied military aircraft based in the Azores, which closed the air gap in the Mid-Atlantic and made operations there equally hazardous.<ref>[https://ahd.mne.gov.pt/nyron/library/catalog/winlibimg.aspx?skey=6684EE5501BE44FBB45311EA98100E2E&doc=57118&img=1699&save=true.] Documentos relativos aos acordos entre Portugal, Inglaterra e Estados Unidos da América para a concessão de facilidades nos Ac̦ores durante a guerra de 1939–1945, Imprensa Nacional, 1946</ref> From June to September 1943 Coastal Command kept up its Bay offensive with operations Musketry, Seaslug and Percussion. By the first week of August 1941 U-boats were sunk in the Bay of Biscay.{{sfn|Costello|Hughes|1977|pp=|p=288}} The Bay offensive was intensified by sending escort and support groups into the Bay but these ships were driven off by German [[Dornier Do 217]] aircraft armed with [[Henschel Hs 293]] guided glide bomb, which claimed several victims.{{Sfn|Blair|1996b|pp=377}}

In September 1943 Dönitz hoped to surprise the Allies by sending the [[Wolfpack Leuthen]] back to the North Atlantic convoy lanes. These U-boats were equipped with [[G7es torpedo|T5 "Zaunkönig"]] acoustic torpedoes, better anti-aircraft guns, a new "Wanze" radar detector and "Afrodite" radar decoys. In an adaptation of their wolfpack tactics, they were ordered first to attack convoy escorts with their acoustic torpedoes before attacking the merchant ships. The group achieved surprise and success in its first attack on convoys [[Convoys ONS 18/ON 202|ONS 18 and ON 202]], but all subsequent attacks were beaten off with heavy loss for the Germans. Other wolfpacks [[Wolfpack Rossbach|Rossbach]], [[Wolfpack Schlieffen|Schlieffen]] and [[Wolfpack Siegfried|Siegfried]] were formed and kept the new campaign going but could achieve little for heavy losses. Only eight&nbsp;ships of 56,000&nbsp;tons and six&nbsp;warships had been sunk for the loss of 39&nbsp;U-boats, a catastrophic loss ratio. In November Dönitz finally recognized wolfpack attacks were not viable anymore in the face of heavy convoy escort and dispersed his U-boats.{{Sfn|Blair|1996b|pp=420-441}}{{Sfn|Showell|2002|p=132-134}}{{sfn|Costello|Hughes|1977|pp=291-293}}
[[File:U-boat Warfare 1939-1945 C3780.jpg|thumb|{{GS|U-459||2}}, a Type XIV supply submarine (known as a "milch cow") sinking after being attacked by a Vickers Wellington]]

From January 1944 onwards, Dönitz tried to preserve his U-Boat strength in order to be able to repel an expected invasion in both Norway and France. The number of patrols by his Atlantic U-boats fell from 41 in January to 10 in May. Since U-boats were still diverted to the Mediterranean or kept in reserve in Norway and since operational losses were high, the number of available U-boats in the Atlantic force sank in the same period from 121 to 89.{{Sfn|Blair|1996b|pp=478-482}} Dönitz had hoped the {{lang|de|elektroboote}} could pick up the offensive on the convoy lanes again in 1944, but the construction of these boats was delayed by shortages of skilled workers and Allied bombing on shipyards and U-boat engine factories. Only in April 1944 was the first type XXI launched and its submerged speed and diving depth proved to be inferior to the designed performance.{{sfn|Costello|Hughes|1977|pp=295-296}}

On [[D-Day]], Atlantic operations were suspended and all available 36 U-boats, later reinforced with another seven, were sent out to confront [[Operation Neptune]]. For the loss of thirteen of their own, these U-boats sank only eight of the 5,339 vessels participating in the [[Operation Overlord|invasion of Normandy]]. Air patrols made operations for U-boats not equipped with a {{lang|de|schnorkel}} impossible and these had to be recalled. A further eleven {{lang|de|schnorkel}} U-boats arrived from Norway in the second week of the invasion, but they sank only two ships for the loss of seven U-boats.{{Sfn|Blair|1996b|pp=579-592}} With the Allied advance in France, the U-boat bases in Brest and Bordeaux were lost in August–September. The other three bases in Lorient, St-Nazaire and La Pallice were evacuated but remained in German hands until the end of the war. No operations could be mounted from these bases and the remaining 30 U-boats were evacuated to Norway. Between 16 May and 1 November 72 U-boats were lost, whilst they could only sink twelve small warships and fourteen merchant ships for 60,000 tons.{{Sfn|Blair|1996b|pp=607-619}}

Norway was too far away from the convoy lanes in order to organise group attacks by the {{lang|de|schnorkel}} U-Boats. In order to keep up the offensive pending the arrival of the {{lang|de|elektroboote}}, 68 patrols were organised from Norway towards British waters between July and December 1944. Only {{lang|de|schnorkel}} Type VII U-boats could be used as Allied air superiority excluded continuous cruising on surface. Sixteen U-boats were lost.{{Sfn|Blair|1996b|pp=627-629}} In the same period, seventeen of the longer range type IX U-boats were sent to Canada and the Azores. These U-boats had also {{lang|de|schnorkels}}, and were equipped with new technology : they had new 'Fliege' and 'Mücke' radar detectors and a new '[[FuG 200 Hohentwiel|Hohentwiel]]' search radar. They sank six warships and nine merchants ships for the loss of seven U-boats.{{Sfn|Blair|1996b|pp=642-654}}[[File:Submarine attack (AWM 304949).jpg|thumb|{{GS|U-848||2}} under attack by a US Navy Consolidated PB4Y-1 Liberator in November 1943]]

In 1945 Dönitz continued with the same approach: type VII {{lang|de|schnorkel}} U-boats mounted 113 patrols to British waters from Norway and Germany. Sixty-five U-boats were lost by the end of the war. Another nineteen type IX U-boats sailed for the Americas; these U-boats sank three small warships and three merchants for the loss of nine of their own. Of the much awaited {{lang|de|elektroboote}}, only five Type XXIII coastal {{lang|de|elektroboote}} made seven patrols in 1945 which sank five small freighters. Only one of the big type XXI {{lang|de|elektroboote}} embarked upon a patrol before the end of the war but it did not see action.{{Sfn|Blair|1996b|pp=662-690}} In the last month of the war, many U-boats fled the Baltic ports as they were overrun by the Russian army. Eight {{lang|de|elektroboote}} and nine other U-boats were sunk by Allied aircraft as they fled towards [[German U-boat bases in occupied Norway|bases in Norway]].{{Sfn|Blair|1996b|p=761}}

The [[Actions of 5–6 May 1945|last actions in American waters]] took place on 5–6 May 1945, which saw the sinking of the steamer {{SS|Black Point|1918|2}} and the destruction of {{GS|U-853|3=2}} and {{GS|U-881|3=2}} in separate incidents. The [[Actions of 7–8 May 1945|last actions of the Battle of the Atlantic]] were on 7–8 May. {{GS|U-320|3=2}} was the last U-boat sunk in action, by an RAF&nbsp;Catalina; while the Norwegian minesweeper {{HNoMS|NYMS 382||2}} and the freighters {{SS|Sneland I||2}} and {{SS|Avondale Park||2}} were torpedoed in separate incidents, hours before the [[End of World War II in Europe|German surrender]].

At the end of the war, 222 U-boats were scuttled by their crews.{{Sfn|Blair|1996b|pp=815-817}} The remaining 174 U-boats, at sea or in port, were surrendered to the Allies. Most were destroyed in ''[[Operation Deadlight]]'' after the war, but some served in Allied navies. Six were in Japan at the time of the German surrender and were captured by the Japanese.{{Sfn|Blair|1996b|pp=818-819}}

===German tactical and technical changes===
The development of torpedoes also improved with the pattern-running {{lang|de|Flächen-Absuch}}-Torpedo ([[FAT (torpedo)|FAT]]), which ran a pre-programmed course criss-crossing the convoy path and the [[G7es torpedo|G7es acoustic torpedo]] (known to the Allies as German Naval Acoustic Torpedo, GNAT),{{sfn|Fitzsimons|1978|p=2615}} which homed on the propeller noise of a target. This was initially very effective, but the Allies quickly developed counter-measures, both tactical ("Step-Aside") and technical ("[[Foxer]]").