I don't know about all of you, but I originally learned about the German Enigma machine as a kid from the ridiculously inaccurate movie U-571. That's uh, not how the Enigma was captured or cracked. In fact, the British Parliament declared it an affront to the real sailors. But the British did capture Enigma machines and parts. And, in October 1942, one sailor risked his life while two more made the ultimate sacrifice to save their peers.
Tommy Brown, First Lt. Tony Fasson, and Able Seaman Colin Grazier were absolute legends.
The Enigma machine
The German Enigma machine allowed the Kriegsmarine, especially the U-boat fleet, to communicate completely in secret. Operators fed a desired message into the machine, got a completely garbled series of letters back, and gave the result to a Morse Code operator.
British and others intercepting signals could listen all they wanted. Without an Enigma machine to decode the message, they had no idea what they had intercepted.
So the British went shopping. In 1941, the British Royal Navy captured machines and codebooks. They fed them to mathematicians and got a window into German communications.
It wasn't perfect. When the convoys avoided too well or when British hunters killed too many wolves out of a German wolf pack, the Germans would change their codes. Mathematicians scrambled to crack the new code every time.
But then something changed.
The fourth rotor
The Enigma machine worked with a series of rotors. If an operator put the rotors in the right position, the encoding and decoding worked. Each rotor supported 26 positions. Initially, the machine used three rotors for 17,576 potential combinations.
When Allied convoys consistently avoided Nazi patrol in 1942, the Kriegsmarine ordered the fourth rotor added. Immediately, the Royal Navy and their mathematicians found themselves shut out. The wolf packs coordinated again through Enigma machines and slaughtered convoys.
The Royal Navy knew something changed and that capturing an intact Enigma, the new codebooks, or potentially even some decrypted communications could reveal how the new configuration worked.
The sinking of U-559 and the ultimate sacrifice
On October 30, 1942, a British plane spotted the German U-boat U-559 on the surface. Nearly every destroyer commander and crew in the Royal Navy was under pressure to capture Enigma materials. So when the plane called in the sighting, five destroyers immediately went on the attack.
The U-boat never suffered a direct hit, but it did take damage from near miss after near miss of depth charges. Leaks slowly filled the stern with water. The crew rushed to the bow to balance the ship, but the engineer declared the situation impossible. The commander sent the boat to the surface.
The British commander of HMS Petard, a destroyer on the chase, ordered his men into the sea after the books. Lieutenant Cmdr. Mark Thornton had a reputation for being hard-driving and potentially crazy. But his men were efficient and quick. The Kriegsmarine sailors, luckily, were not.
As the German sailors abandoned the boat, they failed to properly open the ports to let seawater in. Worse, they didn't dunk the books, which used water soluble ink, in the bucket that was supposed to be handy for just this occasion near the Enigma machine.
Three British sailors swam to the boat, climbed down the conning tower, and got to work. They quickly passed books up to a waiting rowboat, but stayed under too long. The U-boat sank slowly, slowly, and then all at once. Tommy Brown, a canteen assistant, is the only diver to escape the sinking. Two other Brits, First Lt. Tony Fasson and Able Seaman Colin Grazier, were lost.
The books they sacrificed themselves for would save thousands of their fellow sailors and allow convoys to feed millions of otherwise starving Britons.