Found this.
http://boards.history.com/topic/World-War-Ii/October-14-1939/520075253
At 0116 hours on 14 October 1939 the German submarine U-47 fired a spread of three torpedoes at HMS Royal Oak and the British seaplane tender HMS Pegasus lying at anchor in the harbour of Scapa Flow, turned around and fired a stern torpedo at 0121 hours. Prien misidentified the seaplane tender as HMS Repulse and claimed a hit, but a torpedo apparently hit the starboard anchor chain of the battleship and did not damage the ships. At 0123 hours, the U-boat fired a second spread of three torpedoes that hit HMS Royal Oak (Capt. William Gordon Benn, RN) on the starboard side and caused a magazine to blew up. The battleship rolled over and sank in 19 minutes in position 58º55’N, 02º59’W. The ship complement was 1208 officers and men, 833 of them were killed and there were 375 survivors.
Well, it was dark out.
That would make since being that I do remember mention of the Pegasus from the War Cabinets document for the 15th I think.
833 killed.
Thats a big number for a “phony war”