Cryptographic History of Work on the German Naval Enigma

1943 75 machines were produced, rather more than the total number of 4 wheelers produced throughout by us. [This comparison is made to point out the magnitude of their effort and is not meant as a criticism of ours; the whole question of bombes and bombe production is discussed in Chap. ]. In all they produced well over 100 machines which were of the utmost value to us, not only on Naval keys but also in air and army; indeed considerably more than half the total American bombe time went on non-Naval keys. Their whole hearted cooperation and readiness to use their bombes for jobs in which they, as an organization, had no direct interest was always very greatly appreciated by us; a great deal of our success on all keys (Naval, Air and Army) in the last two years of the war was due to their help.

7. In the cryptographic field they adopted from the beginning the clearly correct policy of supplementing our work rather than of attempting to cover the whole field themselves. With this end in view they set up a thoroughly efficient and businesslike organization but did not put in it their best cryptographers. They were taking the lead in Japanese cryptography in which there was an immense field to cover and it would have been wasteful to have put their outstanding technical experts on to the Enigma in which the main problems had been solved and in which we had several years start. Moreover they only intercepted a comparatively small amount of German traffic which was another severe handicap.

8. This policy fitted in admirably with ours and they made many valuable contributions to our joint efforts. Their chief interest was naturally in Shark - it was primarily to help in the U-boat war that they had built their bombes - and their early efforts were entirely concentrated on mastering this. At first we controlled the cribbing, our decisions on what to run being accepted by them; this control was gradually relaxed until in the latter months of the war we handed over the key entirely to them, our contribution being merely to send R.E's into Shark which we had got from other keys.


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