U-550 (Type IXC/40) Blown to the Surface after Torpedoing the Allied Tanker SS Pan Pennsylvania, April 1944,
U.S. Navy photograph in the collections of The Mariners' Museum

Numerous wartime documents reveal that the British, and especially Rodger Winn, discouraged the Americans from overtly using special intelligence to coordinate hunter-killer attacks against U-tankers and U-boats, such as in the capture of U-505. Like many of his superiors at the Admiralty, Winn worried that the Germans might realize that their codes and ciphers were compromised. In his oral history, declassified in 1998, Knowles described the differences between the American and British concepts of using special intelligence: "Ro[d]ger had the feel of the British, naturally, of protecting [special intelligence] at all costs."

Listen to an excerpt from a recently
declassified 1984 interview with Knowles.
U-Tanker U-118 under Attack by U.S. Navy Aircraft, November 5, 1943,
U.S. Navy photograph in the collections of The Mariners' Museum
U-1229 Running with Snorkel Mast Extended, August 20, 1944,
U.S. Navy photograph in the collections of The Mariners' Museum
U-1229 under Attack by U.S. Navy Aircraft, August 20, 1944,
U.S. Navy photograph in the collections of The Mariners' Museum

Indeed, though Winn had many reservations about using special intelligence offensively, the British did attempt limited hunter-killer tactics in areas like the Indian Ocean where the Eastern Fleet was frequently unequipped to support convoys and cope with Axis submarines. In such cases, however, the Admiralty only authorized special intelligence-based hunter-killer operations as a last resort—unlike the U.S. Navy, which treated hunter-killer tactics as a standard operating procedure after 1943.

Though British and American strategies for fighting the Battle of the Atlantic were often at odds, the Allies overcame potentially divisive tensions with the strategic reorganization in 1943. For the rest of the war, Winn and Knowles acted in tandem to unify the Allied anti-submarine commands, though they agreed to disagree on using special intelligence at a tactical level. Winn's tracking room deprived enemy attackers of clear targets by diverting Allied shipping away from danger in the North Atlantic. The Germans responded by seeking targets in less decisive operations areas. Covering the more southerly convoy routes, U.S. Navy escort strength was enhanced because issues of command and control were clarified by the formation of Tenth Fleet. Moving on operational intelligence collected by Kenneth Knowles and his staff, U.S. Navy hunter-killer formations overwhelmed the U-boats.

Essentially, the Battle of the Atlantic was the key campaign that determined the Allied victory in Europe. Holding the Japanese in the Pacific, the Allies concentrated on defeating the European Axis powers first. From the summer of 1943 to the end of the European war in 1945, F-21 and the Admiralty submarine tracking room played a key role in sinking more than seventeen enemy surface vessels (including fifteen blockade runners and two U-boat refueling ships) and a decisive ninety-three Axis submarines (including fifty-four eliminated by U.S. Navy hunter-killer groups). Producing war-winning results, Winn and Knowles were both promoted to the rank of captain by 1945. Due to the efforts of Winn and Knowles and their special intelligence operatives, the Allies secured victory in Europe before the Germans could exploit their growing technological advantages in submarine snorkel propulsion, acoustic homing torpedoes, and radio burst transmissions.

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