Editing Karl Dönitz (section)

===Hunter-killer era===
From mid-June 1943 the technological and industrial superiority of the Allied navies allowed the Americans, Canadians, and British to form [[hunter-killer group]]s consisting of fast anti-submarine escorts and aircraft carriers. The purpose of naval operations changed from avoiding U-boats and safeguarding convoys to seeking them out and destroying them wherever they operated.{{sfn|Milner|2011|p={{page needed|date=January 2022}}}} USN hunter-killer groups operated throughout the Atlantic. [[Argentia]] had been an important base for the naval taskforces until superseded by the [[Royal Canadian Navy]] in early 1943.{{sfn|Milner|1994|pp=24, 28}} U-boat operations were "crushed" by these task forces: 14 were sunk and only two of seven crews operating in Brazilian waters returned to Germany.{{sfn|Milner|1994|p=47}}

Dönitz reacted by deploying his U-boats near the [[Azores]] where land-based aircraft still had difficulty reaching them. In this region he hoped to threaten the Gibraltar–Britain convoy route. Dönitz intended to concentrate his power in a rough arc from [[West Africa]] to [[South America]] and the Caribbean.{{sfn|Milner|2011|p={{page needed|date=January 2022}}}} He hoped to maintain a presence in the western and central Atlantic, reduce losses and await new weapons and anti-detection devices. In this, he failed to "stem the tide of U-boat losses."{{sfn|Milner|1994|p=47}} A large portion of the 39 U-boats deployed on these operations were intercepted.{{sfn|Milner|1994|p=47}} From May 1943, one historian wrote "U-boats rash enough to close with an Atlantic convoy...were simply inviting destruction."{{sfn|Milner|2011|p=178}}
[[File:S7bsu1objfg61.webp|thumb|Karl Donitz and Cemil Cahit Toydemir (July 1943)]]
Dönitz's crews faced danger from the outset. The transit routes through the Bay of Biscay were heavily patrolled by aircraft. From May to December 1943, 25 U-boats were sunk by Coastal Command, more were sunk by the [[USAAF]] and Royal Navy—five and four respectively; with one shared by the navy and Coastal Command.{{sfn|Milner|2011|pp=189–190}} To counter radar aircraft, Dönitz ordered his submarines to group together and merge their powerful anti-aircraft armament together while surfaced and recharging their batteries, after initially ordering the groups to remain surfaced throughout the journey and fight off aerial attackers with gunfire. The decision was to cost BdU heavy casualties. A group of U-boats were more likely to attract a radar contact, and Allied pilots soon learned to swarm their targets.{{sfn|Milner|2011|pp=189, 191}} Dönitz ordered his captains to traverse the Bay under the lee of the neutral Spanish coast, with a sharply rising coast which shielded U-boats from radar. After 4 August 1943, the number of destroyed U-boats fell from one every four days, to one every 27 until June 1944.{{sfn|Milner|2011|pp=192–193}}

US hunter–killer groups extended their patrols to the central Atlantic in the summer. They sank 15 U-boats from June through to August 1943. A number of supply submarines were destroyed crippling the Germans' ability to conduct long range operations. At the end of the summer, practically all supply U-boats had been destroyed.{{sfn|Milner|2011|pp=188–189}} In September 1943, Dönitz ordered his submarines back to the North Atlantic. U-boats were equipped with the [[G7es torpedo]], an acoustic torpedo, which the grand admiral hoped would wrest the technological initiative back. The torpedo was the centrepiece to Dönitz's plan. Great faith was also placed in the installation of {{lang|de|Wanze}} radar to detect aircraft. It was intended as a successor to the [[Metox radar detector]]. A number of his boats were later retrofitted with the [[submarine snorkel]], permitting the submarine to stay submerged.{{sfn|Milner|1994|pp=61–63}} Dönitz placed much faith in the [[Type XXI submarine]]. He accepted that the older submarines were obsolete now that Allied defences in the air were complete. He required a "true submarine", equipped with a snorkel to allow his crews to stay submerged, at least to snorkel-depth, and evade radar-equipped aircraft. Dönitz was pleased with the promised top speed of 18 [[Knot (unit)|knots]].{{sfn|Milner|2011|p=194}}

That month, 21 boats fought a battle with two formations; [[Convoys ONS 18/ON 202]]. The battle was a failure. In October an attack on [[Convoy SC 143]] failed, even with limited air support from the ''Luftwaffe''. The battle with [[Convoys ONS 20/ON 206]] in the same month was a comprehensive defeat. A fourth major battle, [[Convoy SL 138/MKS 28]], developed in the last days of October and ended in another failure for Dönitz. The November battle around [[Convoy SL 139/MKS 30]] ended in the repulse of 29 U-boats with the loss of only a single ship.{{sfn|Syrett|1994|pp=181–229}} Intelligence proved its worth. During the battles of convoys ONS 18/ON 202, Dönitz's admonitions to his commanders allowed the Allied intelligence services to uncover German tactical intentions.{{sfn|Milner|2011|pp=195–196}} Dönitz had tried and failed to push his forces through lethal convoy defences. The hunter-killer groups were called in to hunt the remaining members of the wolfpacks, with predictable results. In mid-December 1943, Dönitz finally conceded not only the Atlantic, but the Gibraltar routes as well.{{sfn|Milner|2011|p=204}}

The hunter-killer and convoy escorts brought the wolfpack era to an end at the close of 1943.{{sfn|Syrett|1994|pp=230–260}} Dönitz resorted to sending out single submarines to the far reaches of the oceans in a bid to escape Allied naval power. In November 1943 he sent the last U-boat into the Gulf of Mexico just after the blackout restrictions were lifted. [[German submarine U-193|''U-193'']] achieved one final success.{{sfn|Wiggins|1995|p=228}} The end of 1943 ended the attempt of the U-boat arm to achieve a strategic victory in the Atlantic. That left only the [[Arctic convoys]] to the [[Soviet Union]]. On Christmas Eve, this became the sole preserve of the U-boats after the dispatch of [[German battleship Scharnhorst|''Scharnhorst'']] at the [[Battle of the North Cape]].{{sfn|Milner|2011|p=204}}

[[File:Bundesarchiv Bild 183-J09741, Trauerfeier für Generaloberst Hans Hube.jpg|thumb|left|From left to right: [[Günther von Kluge|Kluge]], [[Himmler]], Dönitz (with his grand admiral's baton) and [[Wilhelm Keitel|Keitel]] at [[Hans Hube]]'s funeral, 1944]]

Dönitz's plan for 1944 was simply to survive and await the XXI and [[Type XXIII submarine]]s. New radars were on the horizon and a direction finding antenna for ''Naxos'' was scheduled for use. Dönitz established a naval operations scientific staff to focus on more powerful centimetric radars. Production of submarines was streamlined. Parts for eight major sections were fabricated across 60 plants in Europe and assembled at Hamburg, [[Danzig]] and [[Bremen]] to ease the pressure of bombing and congestion at shipyards. The first of the new generation boats were expected by April 1944. Dönitz hoped for 33 per month by September.{{sfn|Milner|2011|pp=205–207}} In early 1944, Dönitz opted to concentrate west of [[Ireland]], at 15 and 17° west, in the hope convoys would come to them. Single boats were still sent to the Mediterranean and [[Indian Ocean]]. With 66 vessels at sea at any one time, and with 200 boats operational, the BdU was still a viable threat and he believed the force could achieve modest success.{{sfn|Milner|2011|pp=205–207}} The U-boats were painfully slow, strategically, operationally and tactically. Crossing the Atlantic took up to a month compared to a week in 1942. Positioning west of Ireland could take several weeks submerged.{{sfn|Milner|2011|pp=205–207}} In the first quarter of 1944, U-boats sank only three of the 3,360 ships that passed south of Ireland. In return 29 crews were lost.{{sfn|Milner|2011|pp=216, 218}}

A major concern to Dönitz was [[Operation Overlord]], the long predicted landing in France, and what role the U-boat arm and surface forces could play in the defence. He was sensitive to a landing on the Bay of Biscay but retained boats there only for operational readiness. Dönitz ended reconnaissance operations in the region. In the BdU war diary he wrote of ending operations since "otherwise the strong enemy air activity will lead to high losses which would only be acceptable if an immediate landing on the Biscay coast were expected. As this is no longer considered an acute danger the boats will remain at readiness in the concrete shelters."{{sfn|Tarrant|1994|p=81}}

[[File:Admirał Karl Donitz i admirał Hellmuth Heye w otoczeniu marynarzy niemieckiej marynarki wojennej (2-2605).jpg|thumb|right|Karl Dönitz with students in July 1944.]]

When the [[D-day landings]] took place on 6 June 1944, the U-boats were ordered into action with the awareness that the western flank of the invasion would be well protected at sea.{{sfn|Tarrant|1994|pp=76, 80–81}} Operational experience with the snorkel was too scant to devise instructions for its use. The narrow, shallow, waters of the [[English Channel]] provided few opportunities for charging the batteries. Dönitz feared the task was impossible.{{sfn|Tarrant|1994|pp=76, 80–81}} The {{lang|de|Holzbein}} group based at Brest, sent 15 submarines into action against the [[Cherbourg]] peninsula landings part of a 36-strong flotilla.{{sfn|Paterson|2001|pp=237–240}} Only eight had snorkels. The seven non-snorkel boats were ordered to attack on the surface.{{sfn|Paterson|2001|pp=237–240}} The BdU war diary entry on 6 June 1944 states that "for those boats without schnorchel this means the last operation".{{sfn|Terraine|1989|p=645}} Of the 15, only five got near to the invasion fleet.{{sfn|Paterson|2001|pp=237–240}} Five of the snorkel boats survived. In exchange for 10 U-boats with the survivors damaged, two [[frigate]]s, four freighters, and one tank landing ship were sunk.{{sfn|Tarrant|1994|pp=80–81}} 22 U-boats were sunk from 6 to 30 June 1944.{{sfn|Hendrie|2006|pp=121–122}} On 5 July 1944, the Allied Operation ''Dredger'' permitted hunter-killer groups to roam the Western Approaches and Biscay making it a "no-go area" for U-boats.{{sfn|Paterson|2001|p=245}} U-boat operations against Normandy landings were a fiasco. Dönitz and the high command had been ignorant of the true scale of the naval D-day effort.{{sfn|Terraine|1989|pp=645–647}} Dönitz claimed his men sank five escorts, 12 merchant ships and four landing craft for 20 submarines and 1,000 men, of whom 238 were rescued. Dönitz's claims underplayed German losses, which were, in fact, 41 submarines from 82 in France, a 50 per cent loss rate.{{sfn|Terraine|1989|p=650}}

[[File:U-Boot-Ehrenmal Möltenort 2 b.jpg|thumb|[[Möltenort U-Boat Memorial]] near [[Kiel]] in northern Germany. Approximately 30,000 men died under Dönitz's command.]]The collapse of the [[Battle of Normandy|German front in Normandy]] left only the bases in [[German-occupied Norway]] nearest to the Atlantic. The newer boats were not forthcoming either. Ninety Type XXI and 31 Type XIII boats were built by the end of 1944. Sixty of the former and 23 of the latter were in service but none were operational. Dönitz was left with the old VIIs to carry the war into 1945. A large number had snorkels, which enabled them to surface only upon reaching port. Submerged, this meant no radio or Enigma communications and far fewer sightings for the Allied intelligence network to exploit. Dönitz ordered his submarines to British coastal waters with some success in November and December 1944, achieving 85,639 tons. Admiral [[Andrew Cunningham, 1st Viscount Cunningham of Hyndhope|Andrew Cunningham]] remarked of the strategy, "We are having a difficult time with the U-boats....the air are about 90 percent out of business and Asdic is failing us." The inshore waters impeded the use of Asdic, which became confused with wrecks, rocks, and tidal swirls. The new types could conceivably have capitalised on these developments but the war was nearly over. On 1 January 1945, Dönitz had 425 submarines; 144 operational. On 1 April 1945, it was 166 from 429. He threw into battle every available weapon as the German Reich collapsed. Dönitz supported the use of [[Human torpedo]]es; the [[Neger (torpedo)|Neger]], [[Marder (submarine)|Marder]], [[Seehund]] and [[Biber (submarine)|Biber]] were all used in [[suicide mission]]s on his orders, perhaps inspired by the Japanese [[Kamikaze]].{{sfn|Terraine|1989|pp=658–659}}

On 30 April 1945 [[Death of Adolf Hitler|Adolf Hitler committed suicide]]. Dönitz succeeded him as head of state. Admiral [[Hans-Georg von Friedeburg]] succeeded Dönitz as commander-in-chief of the {{lang|de|Kriegsmarine}}.{{sfn|Thomas|1990|pp=253, 255}} On 4 May 1945 the [[German surrender at Lüneburg Heath]] took place. Dönitz issued an order to all U-boats to cease combat operations and return to port or surrender to Allied naval vessels. The order was obeyed with a handful of notable exceptions—the [[Actions of 5–6 May 1945]], and [[Actions of 7–8 May 1945]] occurred after the surrender. The surrendered U-boats numbered into the hundreds and were destroyed in the postwar [[Operation Deadlight]]. The U-boat war finally came to an end on 9 May 1945, the date of the [[German Instrument of Surrender]].{{sfn|Rohwer|Hümmelchen|2005|pp=406–407, 418}}