|This example (Serial # 564) is held by the Norwegian Armed Forces Museum in Oslo, Norway. The B-21 was made in both a wooden and metal case model and also had the capability to be connected to an electric typewriter. (Photo courtesy of Reidar Olsen)|
Dirk Rijmenants explains the B-21 operation. "The B-21 was the first real cipher machine that was invented by Boris Hagelin and commercialized by A.B Cryptograph. It all started with some bluff poker when Hagelin told The Swedish General Staff that he had much experience in cipher machines and that he would produce, within six months, a machine that was superior to the Enigma. They agreed and Boris managed to get the machine finished in time. The only resemblance with the Enigma is the keyboard and the lamps.
The B-21 was actually the breakthrough design that started the commercial success for Hagelin. He started with an older design by Arvid Damm - the 'simplified rotors' in a five by five grid. The Enigma had three rotors, each with 26 contacts, one for each letter of the alphabet, and a reflector to return the signal back into the rotors. With Damm's rotors, only two were required and they only used five contacts. Each letter key had a double contact. One contact went to the negative side and the other to the positive side of the power supply. From the other sides of these contacts, one signal goes to the entry of the first rotor and one to the entry of the second rotor. The output of both rotors went to a five by five matrix with 25 lamps (one letter was omitted or combined with another).
The design of these rotors wasn't new but it did a great job of scrambling the electric signals. However, the innovation in the design was how these two rotors were stepped, and this completely new design by Boris Hagelin would be inherent in Hagelin machines for decades to come. The B-21 was the first machine to use the famous pin-wheels. There were four of these pin-wheels with 17, 19, 21 and 23 pins, which stepped with each depression of a keyboard key. The combination of these primes produced a cycle of approximately 1,500,000 before repeating itself. The two left side pin-wheels controlled the left side rotor and the two on the right side the right rotor. If a pin occurred on one pin-wheel OR the other pin-wheel of such a pair, the controlled rotor was advanced one step. This produced a very irregular stepping of the ciphering rotors. The number of possible pin combinations for all pin-wheel together was an enormous 10e24.
The use of these pin wheels would surface in other successful Hagelin designs such as the C-36, M-209 and C(X)-52. The prototype, build in 1925, was approved by the Swedish Army and later it was sold to other countries. The commercial breakthrough, however, was an adapted version for the French Army. This portable machine, designated B-211, had a printing mechanism and could be operated with a crank in case of power failure. The rotor ciphering electric circuit was powered by a battery".
In the B-21 and B211, the four pin-wheels are used only to control the stepping of the ciphering rotors in a complex fashion. In later Hagelin machines such as the C-36, C38/M-209 and C-52, the pins of these pin-wheels were used only to offset a reciprocal alphabet print drum. The CX-52 used the pins for both offsetting the alphabet drum and to control the very irregular stepping, making finally full use of the ingenious pin-wheel design. (Copy by Dirk Rijmenants) When the machine cover is opened, the ciphering mechanism can be seen at the left side. The four big pin-wheels are located at the bottom of that compartment. Right above these pin-wheels is the axle with cogs that transfer the position of the pins into a movement of the ciphering rotors. These are the two small rotors at the top, with five slide contacts at its axle on one side and five pin contacts on the other side. Although they don't look like ordinary rotors they also have an input and output side and the wiring is scrambled. (Copy by Dirk Rijmenants) All photos in this table by John Alexander
Contributors and Credits:
1) John Alexander <jalex_uk(at)ntlworld.com>
2) Dirk Rijmenants. Email: DR Defcom <dr.defcom(at)telenet.be>
3) Reidar Olsen, Norway. E-mail: <trolok45(at)c2i.net>