There were a number of indications that the Bismarck would be attempting a breakout, including recent increased German reconnaissance of the Royal Navy base in Scapa Flow. The German plan to break out into the Atlantic in secret, so as to mount surprise raids on convoy merchant shipping, never seemed to stand a chance. The move into the North Sea had been spotted from Sweden and reported to the British Naval attache, who informed London. By the time Suckling took his picture from around 8,000 metres just after 1pm, triggering a brief anti aircraft alarm, members of the Norwegian resistance had also radioed London and even taken photographs.
Furthermore Admiral Lutjens, in command of Operation Rhine, knew that the Royal Navy knew, because the Germans were reading British radio traffic:
At 1930 the Bismarck weighed anchor and headed north to join the Prinz Eugen and the destroyers outside Kalvanes Bay. The formation then continued on its way. As we slid past the rocky promontories at moderate speed, I was in a small group of the younger officers on the quarterdeck. We wanted to enjoy the Norwegian scenery at close range before we put out into the Atlantic.
While we were standing there, the chief of the fleet staff’s B-Dienst team, Korvettenkapitan Kurt-Werner Reichard, passed by, a piece of paper in his hand. Eager for news from his interesting duty station, we asked him what he had and he readily told us.
It was a secret radio message from B-Dienst headquarters in German, according to which early that morning a British radio transmission had instructed the Royal Air Force to be on the lookout for two German battleships and three destroyers that been reported proceeding on a northerly course. Reichard said that he was taking the message straight to Lutjens.
I must admit that I found this news somewhat of a damper because we junior officers had no idea that the British were aware of Exercise Rhine. Now we knew that we had been “discovered,” and that was something of a shock.
Confidence remained high on the Bismarck, where the news was confined to a small group of officers. The Bismarck was the most powerful battleship yet built “Faster than anything stronger and stronger than anything faster”.
The Royal Navy was now primed for action. When a later reconnaissance confirmed that the Bismarck had left Norway, the hunt was on. Churchill went so far to invite the United States to join in the hunt- he cabled Roosevelt the next day:
Yesterday, twenty-first, Bismarck, Prinz Eugen, and eight merchant ships located in Bergen. Low clouds prevented air attack. Tonight [we find] they have sailed. We have reason to believe a formidable Atlantic raid is intended. Should we fail to catch them going out, your Navy should be able to mark them down for us. King George V, Prince of Wales, Hood, Repulse, and aircraft-carrier Victorious, with ancillary vessels, will be on their track. Give us the news and we will finish the job.
As it turned out, the United States was to play an unexpected role in finding the Bismarck.