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1 September 2007

Subject: Delusions of Intelligence
Date: Thu, 30 Aug 2007 15:08:11 +0200
From: "Frode Weierud" <Frode.Weierud[at]cern.ch>
To: intelforum[at]lists101.his.com

Dear Dr. Ratcliff,

I read your book, Delusions of Intelligence [Enigma, Ultra, and the End of Secure Ciphers], with great interest. A few things were new to me and I found several of the topics you treat of particular interest. On the negative side, I think the Cambridge University Press should have made a better job in helping you straightening out some of the sore points in the text which often is linked with original German terms and expressions. Here are a few examples: Marine, which you have used throughout the text, is closer associated with Handelsmarine (merchant navy) than Kriegsmarine (navy), and entschlüsseln should be translated as decipher instead of "dekeying". It is a pity, but editing specialized texts seems to be a big problem for most publishers, even for publishing houses a reputed as Cambridge University Press.

My question is the following: Why did you not mention in your book the other German cipher machines and devices that were under development and which so easily could have completely disrupted the allied cryptanalytical programs against Germany? I am here thinking of Schlüsselgerät 39 (SG 39),  Schlüsselgerät 41 (SG 41) and especially the new Enigma rotor Lückenfüllerwalze (variable-notch rotor) which was also planned for use in the Enigma replacement machine, Schlüsselgerät 39.

To show how these devices were evaluated at the time I am quoting from a declassified TICOM document available in the open collection of NSA CCH.


German military cryptographers had secure cipher devices under development. It is a paradox that German high-level cryptography was a "practical" failure and at the same time German military cryptographers had so many secure devices in various stages of development.

One simple item alone, a "variable-notch" rotor, would probably have prevented Anglo-American attempts at reading the Enigma after 1942, if it had been produced in quantity and installed. This rotor was called "Lückenfüllerwalze."

An irregular-drive Enigma that would have defied all presently known methods of solution, was being developed. This was called "Cipher Device 39" (Schlüsselgerät 39, abbreviated "SG-39").

A mechanical, portable, keyboard-operated cipher machine, employing an interacting wheel-motion principle applied to Hagelin-type wheels, had been developed and built and partially distributed, which would have been completely secure against reconstruction even if messages were read in depth. This was called "Cipher Device 41" (Schlüsselgerät 41, abbreviated "SG-41").

It was cryptographically superior to its much smaller U.S. Army equivalent device, Converter M-209.


Source: European Axis Signals Intelligence in World War II as Revealed by "TICOM" Investigations and by other Prisoner of War Interrogations and Captured Material, Principally German.

Volume 2 - Notes on German high Level Cryptography and Cryptanalysis,

WDGAS-14, Army Security Agency, 1 May 1946

Other, more technical reports on these devices shows that the evaluation above was correct and that at the time Anglo-American cryptanalytical services would not have been in a position to break these devices on a current basis. The practical use of these devices, knowing the German's often faulty use of their cipher machines, might occasionally have allowed allied cryptanalysts to decipher isolated messages, but on the whole, they probably would have been in the dark.

The development of Schlüsselgerät 39 and Schlüsselgerät 41 started in 1939 and 1941 respectively. The Anglo-American cryptanalytical attacks against Germany were therefore a hair's breath from disaster. What saved the allied programs was the hopelessly uncoordinated German cryptography and the increasing difficulties the Germans experienced with their industrial productions where everybody was fighting for increasingly scarce resources.

I suppose you are fully aware of these German cipher devices because they have been public knowledge for many years now and as a historian in residence at NSA CCH I suppose you consulted their declassified TICOM documents. For a reference here is a link to David Mowry's monograph, "German Cipher Machines of World War II":


        Frode Weierud

[Frode Weierud's CryptoCellar]


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