of the Master Spy That Helped Win World War II (1976, 2000)
The US was of great assistance in avenging the sinking of the HMS Hood, which the Bismarck sank near Iceland; the pride of the Royal Navy was sunk killing over 1500 on board (Britain viewed the HMS Hood in the same manner as the US would view the USS Arizona). British Prime Minister Winston Churchill believed that the Bismarck (plus her supporting ships) could sever the vital Atlantic artery with the US. Britain would eventually commit 8 battleships, 2 aircraft carriers (Atlantic carriers weren't nearly as large as those in the Pacific) with squadrons of airplanes, 11 cruisers, 21 destroyers, and 6 submarines.
Among that formidable force was a US Navy ensign, Leonard Smith, who was part of the American contingent of PBY Catalinas stationed in Northern Ireland, which at the time were the most effective weapon against enemy warships. Britain had nothing like them, and Smith, along with US naval radio detection units and a Coast Guard cutter, would play a huge role in the sinking of the Bismarck . . . although the US involvement would be "scrubbed" from the official documents.
After a mistake in plotting a course, the British eventually figured out that the Bismarck was heading towards the Bay of Biscay. The Home Fleet had wasted quite a bit of fuel and time looking for the Bismarck in the wrong direction, but the US Coast Guard cutter Modoc saved the day for the British. The Modoc was looking for survivors from the Bismarck's attacks and just happened to be in the Bay of Biscay.
Twenty-four hours after the half-hour radio transmission sent by the Bismarck, Smith saw the great battleship through the clouds, and he decided to fly beneath the cloud cover to get a much better look. Almost immediately after clearing the clouds, Smith saw the Bismarck dead ahead, incredibly close, and the battleship's gunners opened fire on the Catalina. Under fire, Smith turned 180 degrees and then sent off a radio message that sealed the fate of the Bismarck, giving precise coordinates and direction. Very soon after receiving Smith's radio message, 15 British Swordfish torpedo bombers took off from the aircraft carrier Ark Royal; the Germans were unaware that these relatively obsolete planes had radar.
On 27 May 1941 the Bismarck was sunk after one-too-many torpedo hits, with the coup-de-grace fired from a British cruiser that had just arrived on the scene. The British military/government and civilian population became re-energized after Churchill announced the sinking of the Bismarck. The sinking of the Bismarck also had a great psychological effect on FDR in that he pushed even harder for more overt US support for Britain. However, America wasn't yet ready for the commitment that FDR envisioned, so FDR kept pressing for more covert support for Britain. The sinking of the Bismarck led to greater radio intelligence sharing/coordination between the US and Britain; FDR's thinking was that if the US helped Britain against the Nazis, the British, with all their colonial possessions in the Pacific, would help the US against Japan if the need arose . . .