M-209 - Compatibility

Introduction

A cipher machine is expensive. The manufacturer may use the backward compatibility as a major selling point. It allows the purcharser to gradually replace the old model by the new one. He is not obliged to replace at once all its equipments.

Thus, Serie C cipher machines designed by Boris Hagelin are all compatible. Cipher machines C-38 and M-209 are compatible with their ancestors C-35 and C-36. The C-446 and C-48 machine are mere variations of the C-38. Similarly, the CX-52 and CD-57 machines are compatible with each other and consistent with previous models C-38 and M-209.

Compatibility between M-209 and C-35/C-36

The Hagelin C-35 and C-36 have only 5 wheels but they use Slide. The first C35/C36 models had immutable number of lugs (they were named “cams”). There is only one cam (lug) by bar, so there is no overlap.

We give below the kicks for each machine. A kick corresponds to the number of lugs front of a wheel.

C-35:                        C-36:
   Wheel 25: kick = 1          Wheel 25: kick = 1
   Wheel 23: kick = 2          Wheel 23: kick = 2
   Wheel 21: kick = 4          Wheel 21: kick = 3
   Wheel 19: kick = 8          Wheel 19: kick = 7
   Wheel 17: kick = 10         Wheel 17: kick = 12

If I want to set a M-209 in compatible mode with a C-36 (for example), I must set the lugs like that:
2-0, 3-0, 3-0, 0-4, 0-4, 0-4, 0-5, 0-5, 0-5, 0-5, 0-5, 0-5, 0-5, 0-6, 0-6, 0-6, 0-6, 0-6, 0-6, 0-6, 0-6, 0-6, 0-6, 0-6, 0-6. The remaining bars (26 and 27) are left without lugs configured (the lugs remain in the zero position).

Unfortunately, the effective Pins and the corresponding letters appearing in the window are different from one model to another. So, if the external key is "AAAAAA", the active pins are "PONMLK" inside M-209. For C36, if the external key is "AAAAA", the active pins are "JIHHG".

Then, we need a translation table to set Pins:

Wheel 25 : 
  M-209       A B C D E F G H I J K L M N O P Q R S T U V X Y Z
  C-35/C-36   U V X Y Z A B C D E F G H I J K L M N O P Q R S T

Wheel 23 :
  M-209       A B C D E F G H I J K L M N O P Q R S T U V X 
  C-35/C-36   S T U V X A B C D E F G H I J K L M N O P Q R
       
Wheel 21 :
  M-209       A B C D E F G H I J K L M N O P Q R S T U
  C-35/C-36   Q R S T U A B C D E F G H I J K L M N O P
       
Wheel 19 :
  M-209       A B C D E F G H I J K L M N O P Q R S 
  C-35/C-36   P Q R S A B C D E F G H I J K L M N O

Wheel 17 :
  M-209       A B C D E F G H I J K L M N O P Q 
  C-35/C-36   N O P Q A B C D E F G H I J K L M

The slide of a C-35/C-36 must be set to Z.

Compatibility between M-209 and C-38/C-446

Basically, a M-209 machine is a C-38. The only notable difference is the absence of slide. This parameter is variable for the C-38, it is fixed (its value is Z) in case of the M-209. If you want to configure a C-38 to be compatible with a M-209, simply configure its slide to Z.

A M-209 has only 27 bars. Some C-38 models have 29 bars.

The machine C-446 is equivalent to a C-38 but with the impression of plain and cipher text.

Compatibility between M-209 and CX-52

Method to set a CX-52 to be compatible with M-209:

1. Transform CX-52 to M-209
1.1. Choose the wheels 26, 25, 46, 38, 34 (in this order).
1.2. Configure the cage.
In case of a C-52, its bars are already compatible with M-209 ones. In case of a CX-52 B (the French model), we must remove the bars 18, 21, 24 and 27. These one are responsible of the irregular bars advancement. We can replace them with bars from 28 to 32.
1.3 Configure alphabets.
We must use regular alphabets (ABC...XYZ). The extern alphabet is written in clockwise order. It starts (with letter A) at the index (the letter which allows to open the lid). The moveable letters of the internal alphabets (plain and crypto) are in front of the engraved letters (these are in alphabet order). We set A in front of A, B in front of B, and so on.
1.4 Configure the slide
The plain and crypto alphabets must be in reverse order and the slide must be set to Z. To do that, set A letter of the left alphabet (the plain one) in front of Z letter of the right alphabet (the crypto one).

2. Configure the internal key
2.1. Set the Lugs: it is straightforward.
2.2. Set the Pins: The setting for the wheels 26 and 25 is identical to the setting of a M-209, but the wheels 23, 21, 19 and 17 are replaced by wheels 46, 42, 38 and 34. Then, we must set the pins configuration twice for each wheel. There is also another difference: numbers are used to index a Pin in case of CX-52 and a letter in case of M-209. A is translated by 01, B by 02, C by 03, and so on.

3. Configure the external key.
The M-209 external key consists only of letters but the CX-52 external key (which appears in the window) is composed of letters and numbers. We must use a translation table. I give it below.

Example:

We use the setting of TM 11-380 1944.

The beginning of the 26-letter check :

Counter  M-209 Window    CX-52 Window              Plain  Cipher
000      AAAAAA          A – A – F -10 -28 – M       A      T
001      BBBBBB          B – B -12 – F – O -26       A      N
002      CCCCCC          C – C – G -12 -30 – N       A      J
003      DDDDDD          D – D -14 – G – P -28       A      U 
004      EEEEEE          E – E - H -14 -32 – O       A      W

Correspondance between M-209 Window and CX-52/CD-57 one :

M-209  Wheels                    CX-52/CD-57
(23,21,19,17)  Wheel 46   Wheel 42   Wheel 38   Wheel 34   
A              F   34     10  P      28  E      M   08
B              12  R      F   32     O   10     26  E
C              G   36     12  Q      30  F      N   10
D              14  S      G   34     P   12     28  F
E              H   38     14  R      32  G      O   12
F              16  T      H   36     Q   14     30  G
G              I   40     16  S      34  H      P   14
H              18  U      I   38     R   16     32  H
I              J   42     18  T      36  I      Q   16
J              20  V      J   40     S   18     34  I
K              K   44     20  U      38  J      A   18
L              22  X      K   42     A   20     02  J
M              L   46     22  A      02  K      B   20
N              24  A      L   02     B   22     04  K
O              M   02     24  B      04  L      C   22
P              26  B      M   04     C   24     06  L
Q              N   04     26  C      06  M      D   24
R              28  C      N   06     D   26
S              O   06     28  D      08  N
T              30  D      O   08
U              P   08     30  E
V              32  E
X              Q   10


Example :
If we set the M-209 external key to "PEOPLE", then the CX-52/CD-57 must be 
set to "P-E-M-M-A-O". Then, if we cipher the text "ATTACKZATZDAWN" we get 
the cipher-text "WUHDU AJRJQ TLRG".

Compatibility between M-209 and CD-57/C-48

The cipher machines CD-57 and C-48 do not have overlaps. The C-48 has only one lug per bar. The CD-57 doesn't have bars but has displacement disks which plays the same role. Only one lug is set by disk.

If I want to set a M-209 to be compatible with a C-48 or a CD-57 I need to set only one lug per bar.

A CD-57 is very similar with a CX-52, so we must use wheels 26, 25, 46, 42, 38 and 34 to be compatible with a M-209.

References

There are Hagelin booklets which describes how to set a Hagelin cipher machine to be compatible with another. Unfortunately, I don't know the titles and references of these booklets.