[2] In the aftermath of World War I the Kretschmer family remained aloof from the political turbulence of the Weimar era.

He mastered the English language and came to respect British education: its practical focus complemented his scientific and theoretical–based German background.

[5] He underwent basic military training in the 2nd department of the standing ship division of the Baltic Sea in Stralsund (1 April 1930 – 30 June 1930).

The Emden made stops in Ceylon, the Philippines, China and Japan; then Guam, South Africa, Angola and Spain on the return journey.

A month after the Emden's return to Wilhelmshaven on 2 December 1931, Kretschmer and his crew mates were promoted to the rank of Fähnrich zur See (midshipman) on 1 January 1932.

[6] During another torpedo training course at Flensburg-Mürwik (27 September – 21 December 1934), Kretschmer received his commission as Leutnant zur See on 1 October 1934.

[Tr 11] On 26 September 1935, he was transferred to the 1st department of the standing ship division of the North Sea in Wilhelmshaven where he served as a company officer until 25 January 1936.

[9] Kretschmer's first operational experience on a submarine was as a lieutenant on the U-35 in 1937 as first watch officer under the command of Klaus Ewerth and then Hans-Rudolf Rösing.

Rösing's successor, Hermann Michahelles, was killed in a car accident and Kretschmer assumed command for two weeks.

Karl Dönitz, Befehlshaber der Unterseeboote (BdU), ordered attacks on Allied shipping at sea, beginning the Battle of the Atlantic.

[20] On his fifth patrol (5–15 December) he was ordered to explore the inner waters around the Orkney Islands and engage any remaining Home Fleet units that had departed from Scapa Flow in the aftermath of Günther Prien's attack.

[22] U-23 departed from Kiel on 8 January 1940 for its sixth war patrol and Schnee had been replaced by Oberleutnant zur See Hans-Dietrich von Tiesenhausen.

[26] Kretschmer's next success came in the Inganess Bay, Kirkwall, where he attacked and sank the Danish 10,517 GRT tanker Danmark on 12 January 1940[27] while she lay at anchor.

[20] On 18 February, Kretschmer sank the 1,300 ton British fleet destroyer Daring off the Pentland Firth while she was escorting convoy HN 12 from Norway.

A single torpedo was fired, then Kretschmer ordered a u-turn and sped away on the surface; the destroyers neither sighted him nor detected him with ASDIC.

[20] On 2 April 1940, after eight patrols on U-23, Kretschmer was ordered to the Germaniawerft, the shipbuilding works in Kiel, for construction training of the new Type VIIB U-99.

[34] On 21 June, his ninth patrol, his boat was damaged by an Arado Ar 196 floatplane from Scharnhorst in the belief U-99 was a British submarine.

[38] Acts of compassion in submarine warfare were "selective and fickle", one historian wrote when describing Kretschmer's rescue of a lone man in a raft.

[48] Kretschmer recommended his helmsman Stabsobersteuermann Heinrich Petersen for the Knight's Cross after twelve war patrols for saving U-99 from enemy detection.

Kretschmer purportedly confined his remarks to the lack of air support from the Luftwaffe, a point Raeder was fully aware of.

[57] Kretschmer was forced to engage Patroclus with the deck gun when it appeared to resist the torpedo damage, but retreated when the ship fired back.

A Short Sunderland appeared briefly, and Kretschmer was forced to accomplish the destruction of the ship with torpedoes, submerged.

Prien's reports were picked up by the Luftwaffe which sent Focke-Wulf Fw 200s from I. Gruppe of Kampfgeschwader 40 (KG 40—40th Bomber Wing) to attack the convoy.

[65] British reports of the action mention a large red glow appearing deep below the surface amid the depth charge explosions.

That same day the British escorts scored another success against the Kriegsmarine when the noted U-boat skipper Joachim Schepke was killed aboard U-100, having been depth charged, rammed and sunk by Vanoc.

Kretschmer's strength was evidently failing in the cold ocean; his own rescue was at the hands of a British sailor who climbed down the nets and plucked him from the water.

Kretschmer was taken separately, but his crew had to negotiate the streets of Liverpool and were subjected to missiles thrown by angry civilians; the city had been heavily bombed and was closely linked with the Atlantic war.

"[73] Of his personality and view of the war it stated, "He gave the impression of being a quiet, deliberate man, and looked more like a student than a U-Boat Captain.

Allied courts and Rahmlow sought justice against Kretschmer after the war, but he was never vigorously pursued for trial for his role in the death of Berndt.

[18] While on holiday in Bavaria in the summer of 1998, Kretschmer died in an accident during a boating expedition on the Danube to celebrate his 50th wedding anniversary, at the age of 86.