User:BtPt50

The British Admiralty had already suspected that a breakout was likely and Bismarck's departure was confirmed for them from a combination of Ultra intelligence (deciphered Enigma code messages), a report from the Swedish cruiser Gotland that had sighted the battleship, and the Norwegian resistance. The latter sent the following message to the British: "A battleship, assumed to be German, passed by Kristiansand heading west, escorted by three destroyers". Three days later, she was photographed by a Spitfire reconnaissance aircraft while resting in a Norwegian fjord (Grimstadfjorden, near Bergen). A subsequent bombing raid by the RAF proved fruitless, as the Germans had already left. Royal Navy cruisers and other warships were deployed to watch the various routes she could take into the Atlantic.

The British learned from Ultra intelligence (deciphered Enigma code messages) of current German air surveillance near the Denmark Strait and of the Royal Navy Home Fleet base as Scapa Flow, and of recent (April 1941) delivery to the Bismarck of charts for the Atlantic. The British decrypted no other naval Enigma messages from or to the Bismarck squadron before the Bismarck was sunk. British radar-equipped cruisers, able to refuel in Iceland, patrolled the Denmark Strait. Unequipped to refuel battle squadrons at sea, the Home Fleet awaited a firm sighting report before its ships deployed. On May 20, 1941, the Swedish cruiser Gotland encountered and tracked the Bismarck battle group steaming northwest past Göteborg. A Norwegian officer in Stockholm learned of Gotland’s sighting report and informed the British naval attaché, who promptly radioed the Admiralty, “Most Immediate. Kattegat today 20th May. At 1500 two large warships escorted by three destroyers, five escort craft, ten or twelve aircraft passed Marstrand course north-west 2058/20th May 1941. B-3 repeat B-3.” B-3 indicated uncertainty about the report's validity, since Gotland's report was more precise and more timely than anything the naval attaché had seen in a year at his station.

Alerted by this report, at 0330 21 May the Admiralty requested air reconnaissance of the Norwegian coast. A Spitfire reconnaissance aircraft found and photographed Bismarck in a fjord (Grimstadfjorden, near Bergen) at 1300, only two hours after Bismarck and Prinz Eugen arrived. With this air intelligence the Home Fleet Battlecruiser Squadron, chiefly comprising the new battleship HMS Prince of Wales and the battlecruiser Hood, sailed that day toward Iceland. Cruisers sailed for stations to cover other approaches.

Many popular books about the Bismarck operation mention a sighting report supposedly radioed by Norwegian agents on 20 May, and supposedly acknowledged by a British reply. This story apparently originated in the 1967 book The Greatest Gamble, which lacks source citations and other authentication to distinguish it from juvenile fiction. No evidence, either direct or circumstantial, supports this story. British and Norwegian authorities categorically deny that secret agents (i.e., HUMINT) were involved before or during the Bismarck operation, and further deny that the Norwegian resistance had radio or other near-real-time communications with Britain and Sweden in May 1941. (Radio links between Britain and the Norwegian resistance were established in 1942.)

Air reconnaissance by the Royal Navy Fleet Air Arm under clouds on 22 May ascertained that the Bismarck had sailed from Bergen. With this intellingence the Home Fleet Battle Fleet, including the battleship HMS King George V and the aircraft carrier Victorious, put to sea. The Battlecruiser Squadron already bound for Iceland was ordered to cover the Denmark Strait. A bombing raid on 22 May by the RAF proved fruitless, as the Germans had already left.