Excerpt from the Wikipedia entry. The entire article is at the link.
Capture of U-505Ten minutes after reversing course, however, on 4 June 1944, 150 miles West of Cape Blanco in French West Africa, Chatelain detected U-505 as it was returning to its base in Brest, France after an 80-day commerce-destroying raid in the Gulf of Guinea. The destroyer loosed one depth charge attack and, guided in for a more accurate drop by circling TBF Avengers from Guadalcanal, she soon made a second. This pattern blasted a hole in the outer hull of the submarine, and rolled the U-boat on its beam ends. Shouts of panic from the conning tower led her inexperienced captain to believe his boat was doomed, so he blew his tanks and surfaced, barely 700 yards from Chatelain. The destroyer fired a torpedo, which missed, and the surfaced submarine then came under the combined fire of the escorts and aircraft, forcing her crew to abandon ship.
Captain Gallery had been waiting and planning for such an opportunity, and having already trained and equipped his boarding parties, ordered Pillsbury's boat to make for the German sub and board her. Under the command of Lieutenant, junior grade Albert David, the party leaped onto the slowly circling submarine and found it abandoned. David and his men quickly captured all important papers and books while closing valves and stopping leaks. As Pillsbury attempted to get a tow-line on her the party managed to stop her engines. By this time a larger salvage group from Guadalcanal arrived, and began the work of preparing U-505 to be towed. After securing the towline and picking up the German survivors from the sea, Guadalcanal started for Bermuda with her priceless prize in tow. Abnaki rendezvoused with the task group and took over towing duties, the group arriving in Bermuda on 19 June after a 2,500-mile tow.
U-505 was the first enemy warship captured on the high seas by the U.S. Navy since 1815. For their daring and skillful teamwork in this remarkable capture, Guadalcanal and her escorts shared in a Presidential Unit Citation. The captured submarine proved to be of inestimable value to American intelligence, and its true fate was kept secret from the Germans until the end of the war. U-505 is the submarine exhibited in the Museum of Science and Industry (Chicago).
Arriving in Norfolk on 22 June 1944, Guadalcanal spent only a short time in port before setting out again on patrol. She departed Norfolk on 15 July and from then until 1 December, she made three anti-submarine cruises in the Western Atlantic. She sailed on 1 December for a training period in waters off Bermuda and Cuba that included refresher landings for pilots of her new squadron, gunnery practice, and anti-submarine warfare drills with Italian submarine R-9. Guadalcanal arrived Mayport, Fla., for carrier qualifications on 15 December and subsequently engaged in further training in Cuban water until 13 February 1945, when she arrived back in Norfolk. After another short training cruise to the Caribbean, she steamed into Mayport on 15 March for a tour of duty as carrier qualification ship, later moving to Pensacola, Florida for similar operations. After qualifying nearly 4,000 pilots, Guadalcanal returned to Norfolk, Va., and decommissioned there on 15 July 1946.