German aerial reconnaissance confirmed that one aircraft carrier, three battleships, and four cruisers remained at anchor in the main British naval base at Scapa Flow, which confirmed to Lütjens that the British were unaware of his operation. On the evening of 20 May, Bismarck and the rest of the flotilla reached the Norwegian coast; the minesweepers were detached and the two raiders and their destroyer escorts continued north. The following morning, radio-intercept officers on board Prinz Eugen picked up a signal ordering British reconnaissance aircraft to search for two battleships and three destroyers northbound off the Norwegian coast.[40] At 7:00 on the 21st, the Germans spotted four unidentified aircraft, which quickly departed.