The UKW-D (field re-wirable reflector) was first introduced in January 1944 by the Luftwaffe of all organisations! It replaced the existing reflectors (UKW-B and UKW-C)
It was sometimes used in conjunction with the Enigma Uhr (which replaced the patch cables at the plug board (Steckerbrett) and was broken within days of introduction by Bletchley Park) as in the Luftwaffe 'Red Key'.
The new rewirable reflector was mounted in place of the existing UKW-B or C, and was rather cumbersome. It required part of the machine to be disassembled. The operators didn't like it and as a result, the wiring was changed only once every 10 days, as per an updated key sheet.
Now the crucial part, at least for the British
Had UKW-D been used with all Enigma machines in the field, it would have posed a serious (and possibly fatal) threat to the British code breakers. Luckily, UKW-D wasn't distributed widely and was therefore only used for specific, important, messages. Like with the Uhr, the Germans had to be able to exchange messages with both UKW-D and non-UKW-D users, so they mixed messages with and without the devices, using the same basic key. This provided long cribs and made breaking both Uhr and UKW-D very easy once the basic key had been broken.
Once again it was German operational procedure which allowed this Enigma to be broken.
A special version of UKW-D was developed for the KM, for use with the four rotor M4 machine, but was only issued to units which had to communicate with the Luftwaffe. Once again the backwards compatibility issue and poor procedure compromised the potential gain in security.
The Luckenfullerwalze (gap-filling wheel) sometimes called the Wahlluckenwalze (selectable gap wheel) really was any code breakers nightmare. This was an Army development of the Enigma machine and had it been produced and distributed in time may well have secured encryption for the foreseeable future, unless the Germans gave the game away themselves.
Cheers
Steve
It was sometimes used in conjunction with the Enigma Uhr (which replaced the patch cables at the plug board (Steckerbrett) and was broken within days of introduction by Bletchley Park) as in the Luftwaffe 'Red Key'.
The new rewirable reflector was mounted in place of the existing UKW-B or C, and was rather cumbersome. It required part of the machine to be disassembled. The operators didn't like it and as a result, the wiring was changed only once every 10 days, as per an updated key sheet.
Now the crucial part, at least for the British
Had UKW-D been used with all Enigma machines in the field, it would have posed a serious (and possibly fatal) threat to the British code breakers. Luckily, UKW-D wasn't distributed widely and was therefore only used for specific, important, messages. Like with the Uhr, the Germans had to be able to exchange messages with both UKW-D and non-UKW-D users, so they mixed messages with and without the devices, using the same basic key. This provided long cribs and made breaking both Uhr and UKW-D very easy once the basic key had been broken.
Once again it was German operational procedure which allowed this Enigma to be broken.
A special version of UKW-D was developed for the KM, for use with the four rotor M4 machine, but was only issued to units which had to communicate with the Luftwaffe. Once again the backwards compatibility issue and poor procedure compromised the potential gain in security.
The Luckenfullerwalze (gap-filling wheel) sometimes called the Wahlluckenwalze (selectable gap wheel) really was any code breakers nightmare. This was an Army development of the Enigma machine and had it been produced and distributed in time may well have secured encryption for the foreseeable future, unless the Germans gave the game away themselves.
Cheers
Steve