Soviet WWII Ground Forces Call Sign Crypto System

This is a reconstruction made by the Finnish Signal Intelligence organisation, RTK (Radiotiedustelukeskus - Radio Interception Central), in June 1943, of a Soviet Ground Forces call sign system.
It was sent to me from Finland by a visitor to this site (thanks!).

The system uses four 10 by 10 squares. The top most, left square contains the dates in the month. The top most, right square is filled by single digits in such a way, that in a row or column, an individual figure only occures once (a so called Latin square). The bottom, left square is identical with the top, right one. Finally, the bottom, right square holds the call signs, 100 in number, made up of three characters (letters only, or letters mixed with figures).

110         9371285604
      5 11  2517608493
8 3        7820953146
    6      0654379218
           1089564732
       9   4163820975
   7       3295041867
           8746192350
     4     6908437521
 2  12      5432716089
9371285604 j6rtxtk5hd3dnryjbCmnqf3uL2uwgi
2517608493 tnjonubnu3xmu1n9np5dxd7f5nzfqi
7820953146 x9ubdm1kbpnhrdy1qdjodjxkrkLstp
0654379218 L1yxyi1bqhmnj4aLwgb1vxtyxjed1s
1089564732 jxeygh3ykpzw53boLzcjjd5fwvbrhk
4163820975 bfngrf2xm4xbnCu7uf9awLxvuhd---
3295041867 8raLyajyttsqLuzurqveoguCLgfamu
8746192350 bwnx9bL8hhgdtaubabn6tomnbwoCCj
6908437521 rzajweLttibuLezo2pvkazuaejjnbh
5432716089 n9er5a8dx67f7aynCC15w5jdbztpww

Each station in a net is assigned a number in the range 00 to 99. Let's say our station has the number '18', and we want to find out the call sign for the 6th of the month (only dates from the 1st up to th 12th are found in the above chart. The higher dates had not been broken yet, or perhaps the chart was compiled on the 12th of June, thus the higher numbered dates hadn't been used yet).
We proceed in the following way. First we locate the date in the top most, left square (bold figure 6), then trace down the same column in the bottom, left square until we reach the first figure of the number assigned to our station (bold figure 1). This is the row in which we are to find our call sign in the bottom, right square. Next, following the same row as the date stands on, we search the top most, right square for the last number assigned to our station (bold figure 8). This indicates the column in the bottom, right square. At the intersection of the correct row and column, we find the call sign, CCj.
Proceeding in a similar way, we find that on the 7th, the call sign to use for the station assigned the number '18', is f3u.

According to my sources, the system was also used sometimes to generate the keys to the PT, or chatter table. The row coordinates for a certain date, were the column of numbers in the bottom, left square, standing in the same column as the date, and the column coordinates, the row of numbers in the top most right square, standing on the same row as the date. For instance, on the 6th the row coordinates to the PT would have been 2693580147 and the column coordinates would have been 0654379218.

© Torbjörn Andersson.Torbjörn Andersson Fecit