In one case, Knowles and his F-21 staff had a key role in capturing a U-boat by exploiting cryptologically-derived special intelligence. On June 4, 1944, a U.S. Navy hunter-killer task group intercepted and captured the U-505 off the coast of Africa. Under the overall command of Captain Daniel V. Gallery, the task group included the escort carrier USS Guadalcanal and five destroyer escorts. Gallery received a detailed briefing from Knowles and other Tenth Fleet officials before departing for the war patrol in May. During this pre-deployment briefing, Gallery requested information which "might be useful" in capturing a U-boat. Although Gallery was not given direct access to raw special intelligence, Knowles provided essential information about U-boat operational patterns and trends in the Guadalcanal operations area. Knowles and other Tenth Fleet staff also provided Gallery with interior U-boat drawings that showed the approximate locations of key controls, valves, and possible scuttling charges. Sailors serving under Gallery used this information to rehearse boarding party procedures. During the Guadalcanal war patrol, Knowles provided Gallery all the tracking data that enabled the hunter-killers to intercept U-505. Using this intelligence, Gallery maneuvered his hunter-killer group into a perfect ambush position.
With Knowles and the F-21 trackers providing specific targeting information, the trackers aboard Guadalcanal also plotted the general origin of some HF/DF fixes on radio transmissions from U-505. Though the U-boat was running submerged at the time, Gallery dispatched aircraft to the suspected location of U-505. As the destroyers moved in for the kill, the aircraft deployed sonobuoys and depth bombs. Eventually, U-505 was acquired on SONAR by one of the screening destroyers in the task group. The destroyers pummeled U-505 with hedgehogs and depth charges until, finally, the U-boat was brought to the surface. As the boat cleared the surface, the skipper of U-505 climbed out of the boat and into the conning tower. Caught in a crossfire and wounded, he gave orders to abandon ship. As the panicked crew of U-505 escaped into the water, Gallery gave the "away boarders" order and his sailors captured the U-505. In a feat of heroism and seamanship, Gallery's men secured and stabilized the foundering U-boat, capturing the contents inside. Gallery and his sailors found a treasure trove of intelligence information aboard U-505, including a variety of key codebooks and charts, two M4 Enigmas, and examples of the German TV Zaunkönig acoustic homing torpedo. Though they had a key role in each phase of the much-vaunted capture of U-505, Knowles and his staff only received a highly classified commendation from Admiral King. Due to Cold War secrecy, Gallery was also unable to reveal the pivotal role of F-21 when he wrote his memoirs of the capture, though he did send Knowles a signed photograph of himself standing in the battered U-505 conning tower. Watch the actual text of messages that Kenneth Knowles and his F-21 staff sent to the U.S. Navy hunter-killer Task Group (TG) 22.3. This information was used by American sailors in the Combat Information Center aboard USS Guadalcanal to pinpoint the location and movements of U-505. Ultimately, the intelligence supplied by F-21 to TG.22.3 resulted in the capture of U-505. This event marked the first time U.S. Navy forces successfully captured an enemy warship on the high seas since the War of 1812.
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