Originally Posted by
jmelson
The Bombes were more directly responsible, as the important traffic telling where U-boats would be, were largely sent by naval Enigma cipher. Britain made several Bombes to break the Enigma codes, then the US helped out with several HUNDRED high-speed bombes built by the NCR company. These ran about 60 times faster than the British version, and by using dozens of machines in parallel, they could solve the arrangement of rotors used at the beginning of the day very quickly. Once that was determined, it did not change for a whole day, and then the machines could be run individually to crack different messages.
If you knew where the U-boats would be, you could either try to sink them, or just route the ocean convoys around them. Since the U-boards were slow, and REALLY slow when running deeply submerged, the ships didn't have to divert very far to avoid the U-boats.
The British used strategies to avoid revealing the messages were being cracked. When they knew a sub would be meeting a tender to refuel, they'd send a patrol plane over that spot, so the crews could not help but know they'd been seen. The Germans must have thought the Brits had an amazing number of patrol planes scouring the oceans for them.
Jon
That was good thinking but they nearly ran out of luck when, after the Bismarck episode in May 1941, it was decided to sink all but one of her supply ships dotted around the Atlantic using the same strategy. Their positions for each day were known so it was just a case of pretending to find them with air patrols, then sinking them. One was to be spared so that the reading of enigma wasn't compromised.
Unfortunately the RN just happened to find this one in the course of normal duties and sank it!
This caused much consternation in the UK and Germany but after an investigation the Germans decided it was not possible to break the code. They continued with that thought for the rest of the war.