AAS 207th Meeting, 8-12 January 2006
Session 1 Preservation of Historical Archives
HAD Special Session, Sunday, 10:00am-1:00pm, January 8, 2006, Maryland C

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[1.05] The Moon and the U-47 in Scapa Flow

B. E. Schaefer (Louisiana S. U.)

The skies above affect historical events here on Earth more than is generally realized. Events during wars are often tied to the Moon through operational requirements for illumination (or dark), high tides (or low), and even links to events in lunar calendars. World War II has many famous battles, commando operations, and naval sorties dictated in date by the Moon. Famous examples are D-Day (needing low tides and Full Moon illumination), the amphibious landing on Tarawa (needing but not getting high tides), El Alamein (requiring Full Moon light for the mine-clearers), the Great Escape from Stalag Luft III (chosen for the stealth possible with a New Moon), Mussolini's invasion of Albania (on Good Friday), and even Rudolf Hess' flight to Scotland (timed by a six-planet conjunction and aided in navigation by the Full Moon). This paper will concentrate on one event for which the Moon provided the primary trick for a major Nazi naval victory, while an aurora saved the British from an even worse disaster. The story is set in Scapa Flow, the huge anchorage in the Orkney Islands that was used as a primary base for the British Navy in blockading the North Sea. During World War I, German submarines had twice tried to slip into Scapa Flow but were sunk both times, and the anchorage later became the last resting place of the scuttled German High Seas Fleet. At the outbreak of World War II, then Commodore Karl Doenitz suggested that his ace U-boat captain consider sneaking into Scapa Flow to loose salvos of torpedoes at all the anchored ships. Captain Gunther Prien of the U-47 took up the challenge after realizing that the British had not completely blocked a narrow inlet. His plan was to surface the submarine and go in over the sunken block ships at the highest of spring tides. Spring tides require a syzygy (New or Full Moon), during which the high tides occur near noon or midnight. To be unobserved by onshore guards, the Moon should not be in the sky illuminating the waters. The requirement for darkness forced the choice of going in around midnight on a New Moon date. But this by itself would not have allowed the U-47 to ride high in the water, so Prien chose a New Moon night where the Moon was closest to Earth in its orbit (at perigee) and the spring tide would be at its extreme high. So, on 13 October 1939, the U-47 surfaced just outside Kirk Sound, scraped through the blocked passage, found the battleship HMS Royal Oak at anchor, and fired two salvos which quickly sank the ship killing 833 sailors. Prien could have continued hunting in the anchorage for more ships, but one of the brightest aurora of the year (which was near a sunspot maximum) started illuminating the waters. Prien wisely withdrew as the U-47 would rapidly have been trapped if spotted under the aurora-light. This disaster was a major propaganda victory for the Nazis and was a heavy blow when the British navy and prestige were soon all that separated England from powerful armies.

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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.