Used by: Armoured troops in the area Mga-Voronovo-Turyshkino, such as the 122nd and 185th tank brigades; 25th, 33rd, 35th, 36th, and 50th tank regiments. March 25th, 1943.
The covers of the booklet are much wider than the pages of the code itself. Between the last page of the code and the back cover, a number of loose sheets are stuck in. These are about as wide as the covers, and thus protude around three of the corners of the code's pages. On the three edges which protude, figures are inscribed, and these serve as coordinates to the squares. By removing one sheet and substituting it with another, a new key is inserted. In the picture above, the sheet with key "a" (the "a" in the top right corner) is inserted.
To encode, one first indicate which page to use by the row of figures at the bottom. It doesn't show that well on the scan, but the pages have cut-outs at the bottom, and the part not cut out, ends over one of the figures at the bottom; this figure is the page indicator. In case of page one, the cut out extends up to - but not including - the first figure, a 7 in case of key sheet "a". Thus, to encode the letter "A" in the top left corner of the code proper, we first indicate the page, which is 7; then the row - by using the column of figures on the right edge of the key sheet - which is 2; finally, we indicate the column - by the row of figures on the top edge of the key sheet - which is 3. "A" turns out as 723 in code. The word in the square below, àâòîìàò (automat, or machine gun) would be 793, àòàê, à (attack) on row three, column three, would be 754 and so on.
Here is a scan of page two, with all key sheets removed. Someone has pencilled out a row and column key on the back cover. Perhaps a default key... To the right is key sheet "b" removed, and now we can also see some additional information. It seems this is the key for March 23rd 1943, and the call signs on this day of the stations in the net using this code are: DYN, PLG, MED, HGL, A7U, and 9N1. "A" now encodes as 116.
