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Ciphering Unit

The Ciphering Unit serves as a converter from open text to plain text and vice versa.

The convertion is being done by electrical impulses that run from contact plugs of keyboard to the electromagnets of printing mechanism through electrical circuits of the Ciphering Unit. The wiring of Ciphering Unit is changed in every step of operation.

The machine can also work as a typewriter. In this situation the wiring of the Ciphering Unit is disconnected from the global circuit and thus the keyboard is directly connected with the printing mechanism.

Cipher Disc

Cipher Discs are intended to build up 26 circuits and change the scheme of their connection in every step of operation. That is done by rotating movement.

The set of discs consists of five cipher discs. These are inserted on the axis in the order given by the daily key. On each end of the axis is another so called solid disc which does not rotate. Inside a cipher disc is inserted a commutation filling which is the real bearer of the permutation.

These 5 cipher discs and 2 solid discs forms a complet of cipher disc circuit.

When ciphering or deciphering, the electrical impuls runs through this circuit. After this those 26 circuits is rebuilt since part of the cipher discs rotates by two steps, part rotates by one step and parts stay put. The consenquence is that in each step the scheme of circuits is changed.

The movement of the disc is controled by pins which are inserted into the Rotor Discs based on a very special key. We will discuss pins later in the chapter, see section Pins.

Commutation Filling

Commutation Filling is a bearer of commutation of the Cipher Disc. It is a wheel (rotor) that is inserted on tight into the discs. When a disc rotates, the Commutation Filling rotates congruently.

The machine is equiped with 26 Commutation Fillings, named A-Z on one side and A-Z on other site. The opperating personel choose one for each Cipher Disc and one for left solid disc based on the daily key. The connection of Commutation Filling is secret and set up during a manufacture of the machine. The right solid disc does not contain a Commutation Filling.

The Commutation Filling consists of two parts bolt together by caxal rivets. Both parts of the filling have 26 flat electrical contacts equaly distributed on the circuit. Contacts of one part is connected by conductors with contacts of second part based on the secret scheme.

The filling can be inserted into the disc by either of its sides and can be seated in any of 26 positions. These positions are named A-Z for easier manipulation. When set, the outer contacts of Commutation Filling match perfectly spring contacts of the Rotor Disc. This is how the Commutation Filling together with the disc construct 26 electrical circuits of the disc.


We have mentioned that the disc can move by 0-2 positions in one step. That is determined by the settings of pins. Pin is a small piece of wood or metal that is inserted into the disc in one of 26 positions. In each of those 26 positions can be a pin. The common situation is that there are about 5 pins in each disc.

In one moment, a single position of each disc is so called active. The machine "looks" only on the active positions and according to that determines how many steps will each disc do. The system is quite complicated, here is the diagram.

We will describe the system in detail later. Just briefly now: disc 3 always makes 1 step. Disc 4,5 and 2 can do zero or one step, disc 1 can do one or two steps. The number of steps depends on the number of arrows pointing into the disc. If the pin is located, the arrow is "destroyed" and the rest of following arrows on the way from that position onwards as well.


A commutator is a body screwed together with the platform of the machine.

It is designed to change the connection of the general circuits before entering the circuits of the Disc Unit.

Inside the commutator, there are two groups of socets, one named INPUT, one named OUTPUT. Each group consists of 26 sockets named A-Z. The operating personnel connects those groups by 26 conductors based on the daily key.