Churchill Barrier No. 1 blocking Kirk Sound
On 14 October 1939, the Royal Navy battleship HMS Royal Oak was sunk at her moorings within the natural harbour of Scapa Flow in a nighttime attack by the German U-boat U-47 under the command of Günther Prien. Shortly before midnight on the 13 October the U-47 had entered Scapa Flow through Kirk Sound between Lamb Holm and the Orkney Mainland. Although the shallow eastern passages had been secured with measures including sunken block ships, booms and anti-submarine nets, Prien was able to navigate the U-47 around the obstructions at high tide. He then launched a surprise torpedo attack on the unsuspecting Royal Navy battleship while it was at anchor in Scapa Flow. The U-47 then escaped seaward using the same channel by navigating between the block ships. In response, First Lord of the Admiralty Winston Churchill ordered the construction of several permanent barriers to prevent any further attacks. Work began in May 1940 and was completed by September 1944.(Thanks are due to Wikipedia for the above details).
