Dönitz was born in Grünau near Berlin, Germany, to Anna Beyer and Emil Dönitz, an engineer, in 1891. Karl had an older brother. In 1910, Dönitz enlisted in the Kaiserliche Marine (“Imperial Navy”).

On 27 September 1913, Dönitz was commissioned as a Leutnant zur See (acting sub-lieutenant). When World War I began, he served on the light cruiser SMS Breslau in the Mediterranean Sea. In August 1914, the Breslau and the battlecruiser SMS Goeben were sold to the Ottoman Navy; the ships were renamed the Midilli and the Yavuz Sultan Selim, respectively. They began operating out of Constantinople, under Rear Admiral Wilhelm Souchon, engaging Russian forces in the Black Sea. On 22 March 1916, Dönitz was promoted to Oberleutnant zur See. He requested a transfer to the submarine forces, which became effective on 1 October 1916. He attended the submariner’s school at Flensburg-Mürwik and passed out on 3 January 1917. He served as watch officer on U-39, and from February 1918 onward as commander of UC-25. On 2 July 1918, he became commander of UB-68, operating in the Mediterranean. On 4 October, after suffering technical difficulties, Dönitz was forced to surface and scuttled his boat. He was captured by the British and remained a prisoner of war until 1919, in 1920 he returned to Germany.

On 27 May 1916, Dönitz married a nurse named Ingeborg Weber (1894–1962), the daughter of German general Erich Weber (1860–1933). They had three children whom they raised as Protestant Christians: daughter Ursula (1917–1990) and sons Klaus (1920–1944) and Peter (1922–1943). Both of Dönitz’s sons were killed during the Second World War. Peter was killed on 19 May 1943 when U-954 was sunk in the North Atlantic with all hands.

Dönitz came to recognise the need for more of these vessels. Only 26 were in commission or under construction that summer. In the time before his command of submarines, he perfected the group tactics that first appealed to him in 1917. At this time Dönitz first expressed his procurement policies. His preference for the submarine fleet was in the production of large numbers of small craft. In contrast to other warships, the fighting power of the U-boat in his opinion did not fluctuate in relation to its size for the torpedo, not the gun, was the machine’s main weapon. Dönitz had a tendency to be critical of larger submarines and listed a number of disadvantages in their production, operation and tactical use. Dönitz recommended the Type VII submarine as the ideal submarine. The boat was reliable and had a range of 6,200 miles. Modifications lengthened this to 8,700 miles.

Dönitz’s promotion earned Hitler his undying loyalty. For Dönitz, Hitler had given him a “true home-coming at last, to a country in which unemployment appeared to have been abolished, the class war no longer tore the nation apart, and the shame of defeat in 1918 was being expunged.” When war came, Dönitz became more firmly wedded to his Nazi faith. Hitler recognised his patriotism, professionalism but above all, his loyalty. Dönitz remained so, long after the war was lost. In so doing, he wilfully ignored the genocidal nature of the regime and claimed ignorance of the Holocaust.

He continued his naval career in the naval arm of the Weimar Republic’s armed forces. On 10 January 1921, he became a Kapitänleutnant (lieutenant) in the new German navy (Vorläufige Reichsmarine). Dönitz commanded torpedo boats, becoming a Korvettenkapitän (lieutenant-commander) on 1 November 1928. On 1 September 1933, he became a Fregattenkapitän (commander) and, in 1934, was put in command of the cruiser Emden, the ship on which cadets and midshipmen took a year-long world cruise as training.

In 1935, the Reichsmarine was renamed Kriegsmarine. Germany was prohibited by the Treaty of Versailles from possessing a submarine fleet. The Anglo-German Naval Agreement of 1935 allowed submarines and he was placed in command of the U-boat flotilla Weddigen, which comprised three boats; U-7; U-8 and; U-9. On 1 September 1935, he was promoted to Kapitän zur See (naval captain).

Dönitz opposed Raeder’s views that surface ships should be given priority in the Kriegsmarine during the war, but in 1935 Dönitz doubted U-boat suitability in a naval trade war on account of their slow speed. This phenomenal contrast with Dönitz’s wartime policy is explained in the 1935 Anglo-German Naval Agreement. The accord was viewed by the navy with optimism, Dönitz included. He remarked, “Britain, in the circumstances, could not possibly be included in the number of potential enemies.” The statement, made after June 1935, was uttered at a time when the naval staff were sure France and the Soviet Union were likely to be Germany’s only enemies. Dönitz’s statement was partially correct. Britain was not foreseen as an immediate enemy, but the navy still held onto a cadre of imperial officers, which along with its Nazi-instigated intake, understood war would be certain in the distant future, perhaps not until the mid-1940s.

Dönitz revived Hermann Bauer’s idea of grouping several submarines together into a Rudeltaktik (“pack tactic”, commonly called “wolfpack”) to overwhelm a merchant convoy’s escorts. Implementation of wolfpacks had been difficult in World War I owing to the limitations of available radios. In the interwar years, Germany had developed ultrahigh frequency transmitters, while the Enigma cipher machine was believed to have made communications secure. A 1922 paper written by Kapitäinleutnant Wessner of the Wehrabteilung (Defence Ministry) pointed to the success of surface attacks at night and the need to coordinate operations with multiple boats to defeat the escorts. Dönitz knew of the paper and improved the ideas suggested by Wessner. This tactic had the added advantage that a submarine on the surface was undetectable by Asdic. Dönitz claimed after the war he would not allow his service to be intimidated by British disclosures about Asdic and the course of the war had proven him right. In reality, Dönitz harboured fears stretching back to 1937 that the new technology would render the U-boat impotent. Dönitz published his ideas on night attacks in January 1939 in a booklet called Die U-Bootwaffe which apparently went unnoticed by the British. The Royal Navy’s overconfidence in Asdic encouraged the Admiralty to suppose it could deal with submarines whatever strategy they adopted—in this they were proven wrong; submarines were difficult to locate and destroy under operational conditions.

In 1939 he expressed his belief that he could win the war with 300 vessels. The Nazi leadership’s rearmament priorities were fundamentally geared to land and aerial warfare. From 1933–1936, the navy was granted only 13 percent of total armament expenditure. The production of U-boats, despite the existing Z Plan, remained low. In 1935 shipyards produced 14 submarines, 21 in 1936, one 1937. In 1938 nine were commissioned and in 1939 18 U-boats were built. Dönitz’s vision may have been misguided. The British had planned for contingency construction programmes for the summer, 1939. At least 78 small escorts and a crash construction programme of “Whale catchers” had been invoked. The British, according to one historian, had taken all the sensible steps necessary to deal with the U-boat menace as it existed in 1939 and were well placed to deal with large numbers of submarines, prior to events in 1940.

On 1 September 1939, Germany invaded Poland. Britain and France soon declared war on Germany, and World War II began. On Sunday 3 September, Dönitz chaired a conference at Wilhelmshaven. At 11:15 am the British Admiralty sent out a signal “Total Germany”. B-Dienst intercepted the message and it was promptly reported to Dönitz. Dönitz paced around the room and his staff purportedly heard him repeatedly say, “My God! So it’s war with England again!”

Hitler’s original orders to wage war only in accordance with the Prize Regulations, were not issued in any altruistic spirit but in the belief hostilities with the Western Allies would be brief. On 23 September 1939, Hitler, on the recommendation of Admiral Raeder, approved that all merchant ships making use of their wireless on being stopped by U-boats should be sunk or captured. This German order marked a considerable step towards unrestricted warfare. Four days later enforcement of Prize Regulations in the North Sea was withdrawn; and on 2 October complete freedom was given to attack darkened ships encountered off the British and French coasts. Two days later the Prize Regulations were cancelled in waters extending as far as 15° West, and on 17 October the German Naval Staff gave U-boats permission to attack without warning all ships identified as hostile. The zone where darkened ships could be attacked with complete freedom was extended to 20° West on 19 October. Practically the only restrictions now placed on U-boats concerned attacks on passenger liners and, on 17 November, they too were allowed to be attacked without warning if clearly identifiable as hostile.

On 1 October 1939, Dönitz became a Konteradmiral (rear admiral) and “Commander of the Submarines” (Befehlshaber der Unterseeboote, BdU). For the first part of the war, despite disagreements with Raeder where best to deploy his men, Dönitz was given considerable operational freedom for his junior rank.

From September–December 1939 U-boats sank 221 ships for 755, 237 gross tons, at the cost of nine U-Boats. Only 47 merchant ships were sunk in the North Atlantic, a tonnage of 249,195. Dönitz had difficulty in organising Wolfpack operations in 1939. A number of his submarines were lost en route to the Atlantic, through either the North Sea and heavily defended English Channel. Torpedo failures plagued commanders during convoy attacks. Along with successes against single ships, Dönitz authorised the abandonment of pack attacks in the autumn. The Norwegian Campaign amplified the defects. Dönitz wrote in May 1940, “I doubt whether men have ever had to rely on such a useless weapon.” He ordered the removal of magnetic pistols in favour of contact fuses and their faulty depth control systems. In no fewer than 40 attacks on Allied warships, not a single sinking was achieved. The statistics show that from the outbreak of war to approximately the spring, 1940, faulty German torpedoes saved 50–60 ships equating to 300,000 GRT.

Dönitz was encouraged in operations against warships by the sinking of aircraft carrier Courageous. On 28 September 1939 he said, “it is not true Britain possesses the means to eliminate the U-boat menace.” The first specific operation, named “Special Operation P”, authorised by Dönitz was Günther Prien’s attack on Scapa Flow which sank a battleship. The attack became a propaganda success though Prien purportedly was unenthusiastic about being used that way. Stephen Roskill wrote, “It is now known that this operation was planned with great care by Admiral Dönitz, who was correctly informed of the weak state of the defences of the eastern entrances. Full credit must also be given to Lieutenant Prien for the nerve and determination with which he put Dönitz’s plan into execution.”

Among the war-crimes charges, Dönitz was accused of waging unrestricted submarine warfare for issuing War Order No. 154 in 1939, and another similar order after the Laconia incident in 1942, not to rescue survivors from ships attacked by submarine. By issuing these two orders, he was found guilty of causing Germany to be in breach of the Second London Naval Treaty of 1936. However, as evidence of similar conduct by the Allies was presented at his trial, his sentence was not assessed on the grounds of this breach of international law.

Dönitz and Raeder accepted the death of the Z Plan upon the outbreak of war. The U-boat programme would be the only portion of it to survive 1939. Both men lobbied Hitler to increase the planned production of submarines to at least 29 per month. The immediate obstacle to the proposals was Hermann Göring, head of the Four Year Plan, commander-in-chief of the Luftwaffe and future successor to Hitler. Göring would not acquiesce and in March 1940 Raeder was forced to drop the figure from 29 to 25, but even that plan proved illusory. In the first half of 1940, two boats were delivered, increased to six in the final half of the year. In 1941 the deliveries increased to 13 to June, and then 20 to December. It was not until late 1941 the number of vessels began to increase quickly. From September 1939 through to March 1940, 15 U-boats were lost—nine to convoy escorts. The impressive tonnage sunk had little impact on the Allied war effort at that point.

In May 1940, 101 ships were sunk—but only nine in the Atlantic—followed by 140 in June; 53 of them in the Atlantic for a total of 585,496 GRT that month. The first six months in 1940 cost Dönitz 15 U-Boats. Until mid-1940 there remained a chronic problem with the reliability of the G7e torpedo. As the battles of Norway and Western Europe raged, the Luftwaffe sank more ships than the U-boats. In May 1940, German aircraft sank 48 ships (158 GRT), three times that of German submarines. The Allied evacuations from western Europe and Scandinavia in June 1940 attracted Allied warships in large numbers, leaving many of the Atlantic convoys travelling through the Western Approaches unprotected. From June 1940, the German submarines began to exact a heavy toll. In the same month, the Luftwaffe sank just 22 ships (195,193 GRT) in a reversal of the previous months.

The U-boat fleet’s successes in 1940 and early 1941 were spearheaded by a small number of highly trained and experienced pre-war commanders. Otto Kretschmer, Joachim Schepke, and Günther Prien were the most famous, but others included Hans Jenisch, Victor Oehrn, Engelbert Endrass, Herbert Schultze and Hans-Rudolf Rösing. Although skilled and with impeccable judgement, the shipping lanes they descended upon were poorly defended. The U-boat force did not escape unscathed. Within the space of several days in March 1941, Prien and Schepke were dead and Kretschmer was a prisoner. All of them fell in battle with a convoy system. The number of boats in the Atlantic remained low. Six fewer existed in May 1940 than in September 1939. In January 1941 there were just six on station in the Atlantic—the lowest during the war, while still suffering from unreliable torpedoes. Dönitz insisted that operations continue while “the smallest prospect of hits” remained.

His sentence on unrestricted submarine warfare was not assessed, because of similar actions by the Allies. In particular, the British Admiralty, on 8 May 1940, had ordered all vessels in the Skagerrak sunk on sight, and Admiral Chester Nimitz, wartime commander-in-chief of the US Pacific Fleet, stated the US Navy had waged unrestricted submarine warfare in the Pacific from the day the US officially entered the war. Thus, Dönitz was not charged of waging unrestricted submarine warfare against unarmed neutral shipping by ordering all ships in designated areas in international waters to be sunk without warning.

Germany’s defeat of Norway gave the U-boats new bases much nearer to their main area of operations off the Western Approaches. The U-boats operated in groups or ‘wolf packs’ which were coordinated by radio from land. With the fall of France, Germany acquired U-boat bases at Lorient, Brest, St Nazaire, and La Pallice/La Rochelle and Bordeaux. This extended the range of Type VIIs. Regardless, the war with Britain continued. The admiral remained sceptical of Operation Sea Lion, a planned invasion and expected a long war. The destruction of seaborne trade became German strategy against Britain after the defeat of the Luftwaffe in the Battle of Britain. Hitler was content with The Blitz and cutting off Britain’s imports. Dönitz gained importance as the prospect of a quick victory faded. Dönitz concentrated groups of U-boats against the convoys and had them attack on the surface at night. In addition the Germans were helped by Italian submarines which in early 1941 actually surpassed the number of German U-boats. Having failed to persuade the Nazi leadership to prioritise U-boat construction, a task made more difficult by military victories in 1940 which convinced many people that Britain would give up the struggle, Dönitz welcomed the deployment of 26 Italian submarines to his force. Dönitz complimented Italian bravery and daring, but was critical of their training and submarine designs. Dönitz remarked they lacked the necessary toughness and discipline and consequently were “of no great assistance to us in the Atlantic.”

The establishment of German bases on the French Atlantic coast allowed for the prospect of aerial support. Small numbers of German aircraft, such as the long-range Focke-Wulf Fw 200, sank a large number of ships in the Atlantic in the last quarter of 1940. In the long term, Göring proved an insurmountable problem in effecting cooperation between the navy and the Luftwaffe. In early 1941, while Göring was on leave, Dönitz approached Hitler and secured from him a single bomber/maritime patrol unit for navy. Göring succeeded in overturning this decision and both Dönitz and Raeder were forced to settle for a specialist maritime air command under Luftwaffe control. Poorly supplied, Fliegerführer Atlantik achieved modest success in 1941, but thereafter failed to have an impact as British counter-measures evolved. Cooperation between the Kriegsmarine and Luftwaffe remained dysfunctional to the war’s end. Göring and his unassailable position at the Reichsluftfahrtministerium (Air Ministry) prevented all but limited collaboration.

Intelligence played an important role in the Battle of the Atlantic. In general, BdU intelligence was poor. Counter-intelligence was not much better. At the height of the battle in mid-1943 some 2,000 signals were sent from the 110 U-Boats at sea. Radio traffic compromised his ciphers by giving the Allies more messages to work with. Furthermore, replies from the boats enabled the Allies to use direction finding (HF/DF, called “Huff-Duff”) to locate a U-boat using its radio, track it and attack it. The over-centralised command structure of BdU and its insistence on micro-managing every aspect of U-boat operations with endless signals provided the Allied navies with enormous intelligence. The enormous “paper chase” [cross-referencing of materials] operations pursued by Allied intelligence agencies was not thought possible by BdU. The Germans did not suspect the Allies had identified the codes broken by B-Dienst. Conversely, when Dönitz suspected the enemy had penetrated his own communications BdU’s response was to suspect internal sabotage and reduce the number of the staff officers to the most reliable, exacerbating the problem of over-centralisation. In contrast to the Allies, the Wehrmacht was suspicious of civilian scientific advisors and generally distrusted outsiders. The Germans were never as open to new ideas or thinking of war in intelligence terms. According to one analyst BdU “lacked imagination and intellectual daring” in the naval war. These Allied advantages failed to avert heavy losses in the June 1940 – May 1941 period, known to U-Boat crews as the “First Happy Time.” In June 1941, 68 ships were sunk in the North Atlantic (318,740 GRT) at a cost of four U-Boats, but the German submarines would not eclipse that number for the remainder of the year. Just 10 transports were sunk in November and December 1941.

On 7 May 1941, the Royal Navy captured the German Arctic meteorological vessel München and took its Enigma machine intact, this allowed the Royal Navy to decode U-boat radio communications in June 1941. Two days later the capture of U-110 was an intelligence coup for the British. The settings for high-level “officer-only” signals, “short-signals” (Kurzsignale) and codes standardising messages to defeat HF/DF fixes by sheer speed were found. Only the Hydra settings for May were missing. The papers were the only stores destroyed by the crew. The capture on 28 June of another weather ship, Lauenburg, enabled British decryption operations to read radio traffic in July 1941. Beginning in August 1941, Bletchley Park operatives could decrypt signals between Dönitz and his U-boats at sea without any restriction. The capture of the U-110 allowed the Admiralty to identify individual boats, their commanders, operational readiness, damage reports, location, type, speed, endurance from working up in the Baltic to Atlantic patrols. On 1 February 1942, the Germans had introduced the M4 cipher machine, which secured communications until it was cracked in December 1942. Even so, the U-boats achieved their best success against the convoys in March 1943, due to an increase in U-boat numbers, and the protection of the shipping lines was in jeopardy. Due to the cracked M4 and the use of radar, the Allies began to send air and surface reinforcements to convoys under threat. The shipping lines were secured, which came as a great surprise to Dönitz. The lack of intelligence and increased numbers of U-boats contributed enormously to Allied losses that year.

Following Hitler’s declaration of war on the United States on 11 December 1941, Dönitz implemented Operation Drumbeat (Unternehmen Paukenschlag). The entry of the United States benefited German submarines in the short term. Dönitz intended to strike close to shore in American and Canadian waters and prevent the convoys—the most effective anti–U-boat system—from ever forming. Dönitz was determined to take advantage of Canadian and American unpreparedness before the situation changed.

Signals security aroused Dönitz’s suspicions during the war. On 12 January 1942 German supply submarine U-459 arrived 800 nautical miles west of Freetown, well clear of convoy lanes. It was scheduled to rendezvous with an Italian submarine, until intercepted by a warship. The German captain’s report coincided with reports of a decrease in sightings and a period of tension between Dönitz and Raeder. The number of U-boats in the Atlantic, by logic, should have increased, not lowered the number of sightings and the reasons for this made Dönitz uneasy. Despite several investigations, the conclusion of the BdU staff was that Engima was impenetrable. His signals officer responded to the U-459 incident with answers ranging from coincidence, direction finding to Italian treachery. General Erich Fellgiebel, Chief Signal Officer of Army High Command and of Supreme Command of Armed Forces (Chef des Heeresnachrichtenwesens), apparently concurred with Dönitz. He concluded that there was “convincing evidence” that, after an “exhaustive investigation” that the Allied codebreakers had been reading high level communications. Other departments in the navy downplayed or dismissed these concerns. They vaguely implied “some components” of Enigma had been compromised, but there was “no real basis for acute anxiety as regards any compromise of operational security.”

The problem inhibiting Dönitz’s plan was a lack of boats. On paper he had 259, but in January 1942, 99 were still undergoing sea trials and 59 were assigned to training flotillas, leaving only 101 on war operations. 35 of these were under repair in port, leaving 66 operational, of which 18 were low on fuel and returning to base, 23 were en route to areas where fuel and torpedoes needed to be conserved, and one was heading to the Mediterranean. Therefore, on 1 January Dönitz had a fighting strength of 16–25 in the Atlantic (six near to Iceland on “Norwegian operations”), three in the Arctic Ocean, three in the Mediterranean and three operating west of Gibraltar. Dönitz was severely limited to what he could accomplish in American waters in an initial offensive.

From 13 January 1942, Dönitz planned to begin a surprise offensive from the Gulf of Saint Lawrence to Cape Hatteras. Unknown to him, ULTRA had read his Enigma signals and knew the position, size, and intentions of his boats, down to the date the operation was scheduled to begin. The attacks, when they came, were not a surprise. Of the 12 U-boats that began the offensive from the Grand Banks southward, just two survived the war. The operation began the Battle of the St. Lawrence, a series of battles which lasted into 1944. It remained possible for a U-boat to operate in the Gulf into 1944, but countermeasures were strong. In 1942, the global ratio of ships-to-U-boats sunk in Canadian waters was 112:1. The global average was 10.3:1. The solitary kill was achieved by the RCAF. Canadian operations, as with American efforts, were a failure during this year.

In 1942 Dönitz summed up his philosophy in one simple paragraph; “The enemy’s shipping constitutes one single, great entity. It is therefore immaterial where a ship is sunk. Once it has been destroyed it has to be replaced by a new ship; and that’s that.” The remark was the green light to unrestricted submarine warfare and began the tonnage war proper. BdU intelligence concluded the Americans could produce 15,300,000 tons of shipping in 1942 and 1943—two million tons under actual production figures. Dönitz always calculated the worst case scenario using the highest figures of enemy production potential. Some 700,000 tons per month needed to be sunk to win the war. The “second happy time” reached a peak in June 1942, with 325,000 tons sunk, up from 311,000 in May, 255,000 in April and the highest since the 327,000 tons sunk in March 1942. With support from the Royal Navy and Royal Canadian Navy, the new convoy systems compelled Dönitz to withdraw his captains to the mid-Atlantic once again. Nevertheless, there was still cause for optimism. B-Dienst had cracked the convoy ciphers and by July 1942 he could call upon 311 boats, 140 operational, to conduct a renewed assault. By October 1942 he had 196 operational from 365. Dönitz’s force finally reached the desired number both he and Raeder had hoped for in 1939. Unaware of it, Dönitz and his men were aided by the ULTRA blackout. The addition of a fourth rotor to the Enigma left radio detection the only way to gather intelligence on dispositions and intentions of the German naval forces. German code breakers had their own success in the capture of the code book to Cipher Code Number 3 from a merchant ship. It was a treble success for the BdU.

November 1942 was a new high in the Atlantic. 134 ships were sunk for 807,754 tons. 119 were destroyed by submarines, 83 (508,707 tons) in the Atlantic. The same month Dönitz suffered strategic defeat. His submarines failed to prevent Operation Torch, even with 196 of them operating in the Atlantic. Dönitz considered it a major self-inflicted defeat. Allied morale radically improved after the victories of Torch, the Second Battle of El Alamein and the Battle of Stalingrad; all occurred within days of one another. The U-boat war was the only military success the Germans enjoyed at the end of the year.

At the end of 1942, Dönitz was faced with the appearance of escort carriers, and long-range aircraft working with convoy escorts. To protect his boats against the latter, he ordered his boats to restrict their operations to the Mid-Atlantic Gap, a stretch of ocean out of the range of land‐based aircraft referred to by the Germans as “the black hole.” Allied air forces had few aircraft equipped with ASV radar for U-Boat detection into April and May 1943, and such units would not exist in Newfoundland until June. Convoys relied on RAF Coastal Command aircraft operating from Northern Ireland and Iceland. The aircraft imposed restraints on U-boat captains, who feared them for their ability to sink a submarine or alert surface warships to their position. In 1942 Coastal Command began forming units combined with ASV and Leigh Light groups to attack U-boats in transit to the Atlantic via the Bay of Biscay, which continued into 1943. The Command was moderately successful after mid-1942.

On 30 January 1943, Dönitz replaced Erich Raeder as Commander-in-Chief of the Navy (Oberbefehlshaber der Kriegsmarine) and Großadmiral (grand admiral) of the Naval High Command (Oberkommando der Marine). In a communique to the navy he announced his intentions to retain practical control of the U-boats and his desire to fight to the end for Hitler. Dönitz’s inability to delegate control of the U-boat service has been construed as a weakness in the U-boat arm, contributing to the perception that Dönitz was an “impatient warrior”, preoccuppied with fighting battles and tactics rather than a strategist or organiser.

New construction procedures, dispensing with prototypes and the abandonment of modifications reduced construction times from 460,000-man hours to 260–300,000 to meet Speer’s quota. In the spring 1944, the Type XXI submarine was scheduled to reach frontline units. In 1943 however, the Combined Bomber Offensive complicated the planned production. Dönitz and Speer were appalled by the destruction of Hamburg, a major construction site. The battles of 1943 and 1944 were fought with the existing VII and Type IX submarines. The type VII remained the backbone of the fleet in 1943.

1943 began with continued tactical success for Dönitz in battle. In January Convoy TM 1 was nearly destroyed. The loss of 100,000 tons of fuel in one convoy represented the most devastating loss percentage of the war—only two of nine tankers reached port. The British 8th Army were forced to ration their fuel for a time, earning Dönitz the gratitude of the Afrika Korps. The Casablanca Conference, held that month, identified the Atlantic as the urgent priority. It was agreed that until the defeat of Dönitz and his men, there could be no amphibious landings in continental Europe. Unknown to Dönitz, Bletchley Park had restored the flow of Enigma information and the Admiralty was able to re-route convoys around wolfpacks. During January and February 1943 information was decrypted within 24 hours proving operationally useful, although this slipped at the end of the second month contributing to German interceptions. Even so, in appalling hunter weather, the Germans sank only 44 ships during the month, even with 100 U-boats at sea, the majority stationed in the mid-Atlantic air gap.

In February 1943 the strength of Allied defences were an ominous sign for Dönitz. The battle of HX 224 was ended upon the intervention of air power from Iceland. Dönitz sent 20 boats to attack SC 118 and both sides suffered heavy losses—11 merchants for three U-boats plus four damaged. It was “what both sides considered one of the hardest fought battles of the Atlantic war.” Despite sending 20 crews into action, Dönitz was concerned that most captains did not press home attacks. The majority of the ships sunk were by one crew, commanded by Siegfried von Forstner—he sank seven.

In March, Convoy SC 121 was attacked by 31 U-boats in two patrol lines. It was the most successful battle of the war for Dönitz. The battle of Convoys HX 229/SC 122 was the largest convoy battle, with 40 U-boats involved. Each operation was successful, but all were fought in the mid-Atlantic. Allied losses reached a peak in March 1943. The Admiralty later issued a report on the matter; “The Germans never came so near [to] disrupting communications between the new world and the old as in the first twenty days of March 1943.” Dönitz later conceded the March battles were to be the U-boats’ last victories. New Allied techniques, tactics and technology began to turn the tide. By April 1943 U-boat morale was reaching a crisis point. 98 new boats were sent into the Atlantic that month, and although the training was thorough the crews were inexperienced and it showed. 15 U-boats were destroyed in March 1943 and another 15 in April. Werner Hartenstein and Johann Mohr were notable casualties over the course of these eight weeks; the former’s decision to rescue survivors of a sunken ship led to Dönitz’s Laconia Order, which later formed part of the criminal case against Dönitz.

For the month of April Allied losses fell to 56 ships of 327,943 tons. In May 1943 the battle reached a climax with the battles of Convoy ONS 5, Convoy SC 129, Convoy SC 130. Throughout the battles only two ships were sunk in convoy in the Atlantic while an air anti-submarine escort was present. Dönitz depended on the surface manoeuvreability of his U-boats to locate targets, assemble wolfpacks and the complicated business of positioning his forces ahead of a convoy for an attack. Allied air power determined where and when U-boats could move freely surfaced. It was the combination of convoy escorts and air power that made the Atlantic unsuitable for pack operations. The US Navy introduced the K-class blimp. They forced a commander to dive to prevent the vehicle marking his position or attacking directly. From 10–24 May 1943, ten convoys passed through the mid-Atlantic. Six of the 370 ships were sunk; three were stragglers. 13 U-boats were sunk; four by warships, seven by aircraft, and two shared.

From mid-June 1943 the technological and industrial superiority of the Allied navies allowed the Americans, Canadians, and British to form hunter-killer groups 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 where ever they operated. 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. 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.

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. 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 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. 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 knots.

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. 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. 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.

The hunter-killer and convoy escorts brought the wolfpack era to an end at the close of 1943. 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. U-193 achieved one final success. 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 Scharnhorst at the Battle of the North Cape.

Dönitz admired Hitler and was vocal about the qualities he perceived in Hitler’s leadership. In August 1943, he praised his foresightedness and confidence; “anyone who thinks he can do better than the Führer is stupid.” Dönitz’s relationship with Hitler strengthened through to the end of the war, particularly after the 20 July plot, for the naval staff officers were not involved; when news of it came there was indignation in the OKM. Even after the war, Dönitz said he could never have joined the conspirators. Dönitz tried to imbue National Socialist ideas among his officers, though the indoctrination of the naval officer corps was not the brainchild of Dönitz, but rather a continuation of the Nazification of the navy begun under his predecessor Raeder. Naval officers were required to attend a five-day education course in Nazi ideology. Dönitz’s loyalty to him and the cause was rewarded by Hitler, who, owing to Dönitz’s leadership, never felt abandoned by the navy. In gratitude, Hitler appointed the navy’s commander as his successor before he committed suicide.

Hitler had issued a policy stating that if a senior officer such as Dönitz lost a son in battle and had other sons in the military, the latter could withdraw from combat and return to civilian life. After Peter’s death Klaus was forbidden to have any combat role and was allowed to leave the military to begin studying to become a naval doctor. He returned to sea and was killed on 13 May 1944; he had persuaded his friends to let him go on the E-boat S-141 for a raid on Selsey on his 24th birthday. The boat was sunk by the French destroyer La Combattante.

Dönitz’s plan for 1944 was simply to survive and await the XXI and Type XXIII submarine. 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 an 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. 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. 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. 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.

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. 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. The Holzbein group based at Brest, sent 15 submarines into action against the Cherbourg peninsula landings part of a 36-strong flotilla. Only eight had snorkels. The seven non-snorkel boats were ordered to attack on the surface. The BdU war diary entry on 6 June 1944 states that “for those boats without schnorchel this means the last operation.” Of the 15, only five got near to the invasion fleet. Five of the snorkel boats survived. In exchange for 10 U-boats with the survivors damaged, two frigates, four freighters, and one tank landing ship were sunk. 24 U-boats were sunk from 6–30 June 1944. 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. 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. 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 percent loss rate.

Dönitz’s influence on military matters was also evident. Hitler acted on Dönitz’s advice in September 1944 to block the Gulf of Finland after Finland abandoned the Axis powers. Operation Tanne Ost was a poorly executed disaster. Dönitz shared Hitler’s senseless strategic judgement—with the Courland Pocket on the verge of collapse, and the air and army forces requesting a withdrawal, the two men were preoccupied in planning an attack on an isolated island in the far north. Hitler’s willingness to listen to the naval commander was based on his high opinion of the navy’s usefulness at this time. It reinforced isolated coastal garrisons along the Baltic and evacuated thousands of German soldiers and civilians in order that they might continue to participate in the war effort into the spring of 1945.

Through 1944 and 1945, the Dönitz-initiated Operation Hannibal, which had the distinction of being the largest naval evacuation in history. The Baltic Fleet was presented with a mass of targets, the subsequent Soviet submarine Baltic Sea campaign in 1944 and Soviet naval Baltic Sea campaign in 1945 inflicted grievous losses during Hannibal. The most notable was the sinking of the MV Wilhelm Gustloff by a Soviet submarine. The liner had nearly 10,000 people on board. The evacuations continued after the surrender. From 3 to 9 May 1945, 81,000 of the 150,000 persons waiting on the Hel Peninsula were evacuated without loss. Albrecht Brandi, commander of the eastern Baltic, initiated a counter operation, the Gulf of Finland campaign, but failed to have an impact.

Dönitz contributed to the spread of Nazism within the Kriegsmarine. He insisted that officers share his political views and, as head of the Kriegsmarine, formally joined the Nazi Party on 1 February 1944, as member 9,664,999. He was awarded the Golden Party Badge for his loyalty to the party later that year. Dönitz’s influence over naval officers contributed to none joining the attempts to kill Hitler.

From an ideological standpoint, Dönitz was anti-Marxist and antisemitic who believed that Germany needed to fight the “poison of Jewry”. Several anti-Semitic statements by Dönitz are known. When Sweden closed its international waters to Germany, he blamed this action on their fear and dependence on “international Jewish capital.” In August 1944, he declared, “I would rather eat dirt than see my grandchildren grow up in the filthy, poisonous atmosphere of Jewry.”

The collapse of the German front in Normandy left only the bases in German-occupied Norway nearest to the Atlantic. The newer boats were not forthcoming either. 90 XXI and 31 XIII’s were built by the end of 1944. 60 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 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 torpedoes; the Neger, Marder, Seehund and Biber were all used in suicide missions on his orders, perhaps inspired by the Japanese Kamikaze.

On 30 April 1945 Adolf Hitler committed suicide. Dönitz succeeded him as head of state and Führer. Admiral Hans-Georg von Friedeburg succeeded Dönitz as commander-in-chief of the Kriegsmarine. 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 8 May 1945, the date of the German Instrument of Surrender.

In the final days of the war, after Hitler had taken refuge in the Führerbunker beneath the Reich Chancellery garden in Berlin, Reichsmarschall Hermann Göring was considered the obvious successor to Hitler, followed by Reichsführer-SS Heinrich Himmler. Göring, however, infuriated Hitler by radioing him in Berlin asking for permission to assume leadership of the Reich. Himmler also tried to seize power by entering into negotiations with Count Bernadotte. On 28 April 1945, the BBC reported Himmler had offered surrender to the western Allies and that the offer had been declined.

From mid-April 1945, Dönitz and elements of what remained of the Reich government moved into the buildings of the Stadtheide Barracks in Plön. In his last will and testament, dated 29 April 1945, Hitler named Dönitz his successor as Staatsoberhaupt (Head of State), with the titles of Reichspräsident (President) and Supreme Commander of the Armed Forces. The same document named Propaganda Minister Joseph Goebbels as Head of Government with the title of Reichskanzler (Chancellor). Furthermore, Hitler declared both Göring and Himmler traitors and expelled them from the party. He killed himself on 30 April.

On 1 May, the day after Hitler’s own suicide, Goebbels committed suicide. Dönitz thus became the sole representative of the collapsing German Reich. On 2 May, the new government of the Reich fled to Flensburg-Mürwik where he remained until his arrest on 23 May 1945. That night, 2 May, Dönitz made a nationwide radio address in which he announced Hitler’s death and said the war would continue in the East “to save Germany from destruction by the advancing Bolshevik enemy.”

On 25 February 1945, Hitler asked Dönitz whether the Geneva Convention should be denounced. Hitler’s motives were twofold. The first was that reprisals could be taken against Western Allied prisoners of war; second, it would deter German forces from surrendering to the Western Allies, as was happening on the Eastern Front where the convention was in abeyance. Instead of arguing the conventions should never be denounced, Dönitz suggested it was not expedient to do so, so the court found against him on this issue; but as the convention was not denounced by Germany, and British prisoners in camps under Dönitz’s jurisdiction were treated strictly according to the Convention, the Court considered these mitigating circumstances.

Even during his imprisonment, after Nuremberg, with the crimes of the Nazi state well-known, Dönitz remained an antisemite. In April 1953, he told Speer that if it was the choice of the Americans and not the Jews, he would have been released.

Dönitz was released on 1 October 1956 and retired to the small village of Aumühle in Schleswig-Holstein in northern West Germany. There, he worked on two books. His memoirs, Zehn Jahre, Zwanzig Tage (Memoirs: Ten Years and Twenty Days), were released in Germany in 1958 and became available in an English translation the following year. This book recounted Dönitz’s experiences as U-boat commander (10 years) and President of Germany (20 days). In it, Dönitz explains the Nazi regime as a product of its time, but argues he was not a politician and thus not morally responsible for many of the regime’s crimes. He likewise criticizes dictatorship as a fundamentally flawed form of government and blames it for many of the Nazi era’s failings. Historian Alan P. Rems has written that Dönitz’s memoirs are unconvincing and that “unimpeded by a meaningful Nuremberg verdict, Dönitz fashioned a legend that could be embraced by the most unregenerate Nazis as well as credulous Allied officers who accepted his sanitized version of history and showered Dönitz with letters of support as a wronged brother-in-arms”.

Dönitz’s second book, Mein wechselvolles Leben (My Ever-Changing Life) is less known, perhaps because it deals with the events of his life before 1934. This book was first published in 1968, and a new edition was released in 1998 with the revised title Mein soldatisches Leben (My Martial Life). In 1973, he appeared in the Thames Television production The World at War, in one of his few television appearances.

Dönitz was unrepentant regarding his role in World War II, saying that he had acted at all times out of duty to his nation. He lived out the rest of his life in relative obscurity in Aumühle, occasionally corresponding with collectors of German naval history, and died there of a heart attack on 24 December 1980. As the last German officer with the rank of Großadmiral (grand admiral), he was honoured by many former servicemen and foreign naval officers who came to pay their respects at his funeral on 6 January 1981. He was buried in Waldfriedhof Cemetery in Aumühle without military honours, and service members were not allowed to wear uniforms to the funeral. Also in attendance were over 100 holders of the Knight’s Cross of the Iron Cross.