U-559.

Should have been about it's capture:

U-559 U-BOAT CODES ARE BROKEN

Even when Bletchley Park began to decipher encrypted Nazi messages, the U-boat version of Enigma proved much more difficult. Not until 1943, after British sailors drowned trying to recover an Enigma machine, were U-boat codes broken on a regular basis.

It wasn't an easy chase on October 30, 1942. HMS Petard and three other British destroyers were pursuing a Nazi sub in the Mediterranean Sea, not far from the Egyptian shore. U-559 was proving why U-boats were so dangerous. She was elusive. The chase lasted 16 hours before U-559's commander decided to scuttle his damaged ship about 70 miles north of the Nile Delta. (Follow this link to a map where U-559 went down. Look in the lower right-hand corner.)

Demonstrating courage that is hard to comprehend, three young men swam from Petard to U-559. Lt. Tony Fasson, Able Seaman Colin Grazier, and Canteen Assistant Tommy Brown descend into the sinking submarine. They wanted to retrieve the Enigma machine.

They could not remove U-559's Enigma from its mount. But with Brown at the top of the stairs, water streaming into the stricken vessel, Fasson and Grazier quickly passed the "Wetterkurzschlüssel" (short signal weather code) and the "Kurzsignalheft" (short signal code book) up to Brown who threw them into his whaleboat.

With death by drowning a near certainty if they didn't immediately leave the ship, Fasson and Grazier continued to gather Enigma documents, keypads and codes. Brown threw it all into the skiff. Barely a blink of an eye after Brown had the priceless Nazi codes on his whaleboat, U-559 went to the bottom, 70 miles from Port Said. Fasson and Grazier went down with her.

Tommy Brown, the Canteen Assistant, turned over one of the most important finds of WWII. He was 16 years old. Wanting to fight for his country, he had lied about his age.

Fasson and Grazier received Britain's second-highest honor for bravery, the George Cross. Brown received the George Medal. Two years later Brown was also dead. He died trying to rescue his two sisters from their burning slum tenement.

U-559's soaked Enigma machine turned out to be an even-more astounding recovery than anyone could have known. It contained the keys to the major German U-boat codes "Shark and Triton" - codes that Bletchley Park had not been able to decipher. Once Bletchley Park realized that the weather signals could be decoded with a four-rotor Enigma with the fourth wheel set on "A" (thus running in the Enigma equivalent of "idle"), they could reverse-engineer the wiring of the fourth wheel. THIS was the REAL achievement of the three valiant Englishmen.