The Battle of Britain Five Months That Changed History, May—October 1940 by James Holland (z-lib.org).epub

Although he had demonstrated his promise during war games before the
war, it was in October that Günther really made his name. The British
Home Fleet was berthed at Scapa Flow, its base in the Orkneys, but Günther
managed to creep U-47 in and sink the Royal Oak. It was a huge coup for
Germany and particularly Dönitz’s U-boat arm, and Goebbels’s propaganda
team wasted no time in making the most of it. By the time U-47 arrived
back in Wilhelmshaven on 17 October, Prien’s name and that of his boat
were known throughout Germany, and waiting on the quay were Raeder
and Dönitz. The crew were then flown to Tempelhof in Berlin, where
thousands waited to cheer them. From there they were bundled into a
motorcade to the smartest hotel in town, their route lined by more cheering
Berliners desperate to see the new naval heroes. There was even lunch with
Hitler at the Reich Chancellery, where the Führer presented Günther with
the new German award for extreme valour, the Knight’s Cross of the Iron
Cross.
Hitler had already been won round to Dönitz’s persuasive arguments for
more U-boats, but there is no doubt that it was the sinking of the battleship
the Royal Oak that really caught the Führer’s imagination and convinced
him of the potential carnage large numbers of U-boats could cause.
Since those dizzy days, the U-boat arm had continued to sink plenty of
ships – 177 in fact – but there were not yet enough U-boats to really make a
difference. But in April the U-boats had been withdrawn from the Atlantic
and sent to Norway instead, where U-47’s fortunes – and those of the entire
U-boat arm – had waned. Part of the reason was faulty torpedoes. U-boats
kept firing only to find their torpedoes never exploded. Most of the
torpedoes they used were detonated by a magnetic pistol, so that as they
reached a target the magnetic force of the ship would detonate them. On 15
April, U-47 had been inside Vaagsfjörd and had discovered three large
transport ships plus three smaller ones and two cruisers – a massive
150,000-ton target that would have eclipsed the Royal Oak by some margin.
None of its torpedoes exploded, however. Later that night, Günther fired
another four at targets that were sitting ducks. Again, not one exploded. He
was outraged at this golden opportunity missed, but then insult was added
to injury when U-47 ran aground. It managed to break free but cracked the
starboard diesel engine in the process. This left Günther with no choice but
to abort the patrol. On the way home, the U-boat came across the battleship
HMS Warspite, escorted by two destroyers. Günther fired two torpedoes but