[Note 1] Under Prien's command, the submarine U-47 was credited with sinking over 30 Allied ships totalling about 200,000 gross register tons (GRT), along with the British battleship HMS Royal Oak at anchor in the Home Fleet's anchorage in Scapa Flow.

[4] After eight years of work and study as a seaman, rising from cabin boy on a sailing ship, Prien passed the required examinations and became the fourth officer on a passenger liner,[2] the SS Hamburg.

[2] Unable to find work due to the severe contraction of the German shipping industry during the Great Depression, he was forced to turn to the Freiwilliger Arbeitsdienst ('Voluntary Labour Service', FAD).

[2][9] Prien received his military basic training in the 2nd company in the 2nd department of the standing ship division of the Baltic Sea in Stralsund (16 January 1933 – 31 March 1933).

[12] On 1 October 1939, Karl Dönitz became a Konteradmiral (rear admiral) and "Commander of the Submarines" (Befehlshaber der Unterseeboote, BdU).

[16] Dönitz was attracted to the prospect of attacking the Royal Navy anchorage at Scapa Flow at the outbreak of war, to win a victory for his command.

[20] His watch officers spotted a merchant ship and Prien dived to avoid it, but shadowed the vessel and carried out a practice attack.

[24] The Home Fleet did not return to Scapa Flow until March 1940, until the entry points were closed and air defences improved.

The reason, given by 1st watch officer Engelbert Endrass for this, was the sight of Prien's demeanour as U-47 entered Scapa Flow, "his frowning face and hunched shoulders reminded him of a bull in a ring.

[37] The historian Riederer argues that Sonderunternehmen P (Special Operation P), the codename for the attack on Scapa Flow, was very likely predominantly motivated by Nazi propaganda.

Following World War I, the German High Seas Fleet was interned at Scapa Flow under the terms of the Armistice whilst negotiations took place over the fate of the ships.

Whilst the internment was considered a national humiliation by the Kriegsmarine, the scuttling of the fleet was romanticised as an act ridding the navy of the shame associated with the Kiel mutiny of 3 November 1918.

When the periscope cleared the surface, Prien observed what he believed major damage to the stern of the cruiser, her starboard torpedo launchers dislodged and an aircraft tilted.

[42] From convoy OB 46, 37 sailors died aboard SS Navasota, another 45 were rescued by other merchant vessels Escapade and Clan Farquhar.

U-boat commanders, determined to enter the ranks of "aces" such as Prien, were prepared to take greater risks, most often attacking at night on the surface—the Admiralty noted that by February 1940 these reached 58 percent.

[44][50] The boat formed part of a 28-strong fleet, practically the entire operational force, committed to waters off the Norwegian and British coast.

The BdU's opposition, the Royal Navy Submarine Service, achieved some success: the Karlsruhe was crippled and scuttled off Kristiansand.

While on manoeuvres to fire his stern torpedo on the surface, he ran aground damaging his starboard diesel engine as he attempted to break free.

"[52] A full report was made by Prien: "we found ourselves equipped with a torpedo which refused to function in northern waters either with contact or magnetic pistols.

This patrol, again Kraus served as 1st watch officer, started and ended in Kiel and targeted the shipping routes in the North Atlantic and the Bay of Biscay west of the English Channel.

Upon the conclusion of the patrol, which had taken U-47 into the North Atlantic west of the Hebrides, Prien was ordered to the U-boat base at Lorient, in occupied France where it arrived on 26 September 1940.

[68] Dönitz ordered Prien to act as a weather-boat at a point 23° west, mainly for Luftwaffe air fleets engaged in the Battle of Britain.

[73] Heinz Rühmann, Hans Brausewetter and Josef Sieber sang a persiflage of the 1939 song "Das kann doch einen Seemann nicht erschüttern" ("That won't shake a sailor"), written by Michael Jary from the film Paradies der Junggesellen—Bachelor's Paradise, on occasion of the Oak Leaves presentation to Prien.

The reworded lyrics are "Das muss den ersten Seelord doch erschüttern" ("That must shake the First Sea Lord", alluding to Winston Churchill).

[86] U-47 has generally been thought to have been sunk by the British destroyer HMS Wolverine west of Ireland; the submarine was attacked by Wolverine and HMS Verity, which took turns covering each other's ASDIC blind spots and dropping patterns of depth charges until U-47 rose almost to the surface before sinking and then exploded with an orange flash visible from the surface.

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

[87] Churchill had personally announced it to the House of Commons, and propaganda broadcasts to Germany had repeatedly taunted listeners with the question "Where is Prien?"

[91] The announcement was made in the Wehrmachtbericht on 24 May 1941 stating: "The U-boat under the command of Korvettenkapitän Günter Prien did not return from his last patrol against the enemy.

To offset the negative impact his death might have on the German population, the message was hidden among the information about the tonnage sunk by U-boats.

[93] According to one biographer, in contrast with Kretschmer, Prien was purportedly a strict disciplinarian who rarely allowed humanity to compromise or interfere with the running of his boat.