French Army C-36: Conclusion () ()

Home Page
C-36 Home Page
  • 1. Introduction.
  • 2. Machine operation
  • 3. The pre-war period
  • 4. The start of the war
  • 5. The Vichy period
  • 6. The Allied period
  • 7. The post-war period
  • 8. Conclusion
  • Appendix

Conclusion

Machine operation

The research I have conducted allows for a complete description of the workings of the C-36. I was thus able to create a simulator that decrypts encrypted messages using an authentic machine. I was also able to decide on the operational details of the version of the machine used during WWII. Thus, there is no doubt that the configuration of the lugs is A (Table 2). This supposition is confirmed not only by the inspection of a machine remaining in the state in which it was in 1940, but also by the decryption of a cryptogram from 1941 and finally by three key tables from 1944 (Le zouave du pont de l’Alma a dit). The other configurations were not used until after the war. Configuration A was never used again because it was the one that offered the least security.

How many machines were manufactured?

Research in the SHD archives also confirms that France never ordered 5,000 C-36s from Mr. Hagelin's firm as the latter claimed. At most, France ordered 3,000 machines to equip its 100 divisions. However, it is more likely only 2,000 were received.

A not very safe machine

If we observe the interior of a C-36, it is a pure mechanical marvel. Unfortunately, the security it offered was weak even at the time of its creation and entry into service (1940). A simple crib of ten characters would overcome it.

Revolutionary machine, ancestor of the C series

Nonetheless, this revolutionary machine allowed Mr. Hagelin, its creator, to design its worthy descendant: the M-209, the most widely used cipher machine in the world. Even in the French Army, the M-209 had replaced the C-36 by 1944. When used properly, the M-209 offers excellent security [1], which is possibly even superior to that of the Enigma. Finally, the CX-52 (taking the serious models), well used, is unbreakable.

Short operational life

The operational history of the C-36 was relatively short. It was put into service just before the start of the French campaign (April 1940). This period was so short that the Germans did not have time to exploit its weaknesses. Then it was only used on wired networks during the Vichy period and was therefore immune to enemy eavesdropping. After the Allies landed in North Africa, it was used again during the campaign in Tunisia and possibly during the campaign in Italy. It was also used during the training of the Free French Army. In all cases, its use was limited to tactical messages. The strategic messages were encrypted with the modified B-211, which ensured complete security. Little by little, the weaknesses of the C-36 surfaced, and the operating procedures then became progressively more complex to try to compensate for its lack of security. The Germans were able to read the C-36 messages like an open book (Le zouave du pont de l’Alma m’a dit). Gradually the C-36 was replaced by the M-209 supplied by the Americans. At the end of July 1944, the C-36 was withdrawn from active service in the French Army that landed in Provence. It was never to find itself in a theater of war again.

The C-36 or the weakness of French cryptography

The use of the C-36 (and first B-211 model) corresponds to the low water of French cryptology. During World War I, France listened to the world (Delhez 2014). After the Second World War, following the practices learned from the Americans and British and the interrogation of German prisoners, the cryptological level of France advanced. Ultimately, France in the 1960s will manufacture the world's f irst fully electronic encryption machine, Myosotis, whose level of security, tested by the Americans, will satisfy the highest security level of NATO (Ameil, Vasseur, Ruggiu 2004).

Footnote:
[1] As proof, the Americans continued to use the M-209 during the Korean War (1950-1953).

References

  • Bouchaudy, J-F, 2019. Genuine French WWII M-209 cryptograms, Cryptologia, 43:5, 359-371, DOI: 10.1080/01611194.2019.1596180
  • Delhez, JC, 2014. La France espionne le monde (1914-1919) Les exploits des briseurs de codes. Editions ECONOMICA, Paris.

Web Links

  • Ameil, X, Vasseur, J-P, Ruggiu, G, 2004. Histoire de la machine Myosotis. Actes du septième Colloque sur l'Histoire de l'Informatique et des Transmissions. This article is present on ARCSI’s web site (link).