Скапа-Флоу
On 14 October 1939, the Royal Navy battleship was sunk at her moorings within the natural harbour of Scapa Flow, by the under the command of Günther Prien. "U-47" had entered Scapa Flow through Holm Sound, just to the north of Burray, one of several eastern entrances to Scapa Flow. The eastern passages were protected by measures including sunken block ships, booms and anti-submarine nets, but "U-47" entered at night at high tide by navigating between the block ships.