Cryptographic History of Work on the German Naval Enigma

break it would not be justified by the results obtained.

35. This abandonment of throw-ons by Porpoise and Grampus further reduced the non-cribbing cryptographic work in the section and led to another staff reduction, Chamberlain and Ashcroft joining Newman's section. Chamberlain for some time had been working largely on J.N.A. 20 and there was not enough to keep either him or Ashcroft profitably employed; Newman's section was rapidly expanding and in great need of more good and experienced cryptographers so the transfers were clearly right - we should, I think have made them earlier. Joan Clarke, who had formerly been one of the best Banburists in the section, now joined Mahon, Pendered and Noskwith and these four coped with the whole of the cryptographic work for the rest of the war. This was a very fine achievement and meant extremely hard work for all four: 6 major keys (Dolphin, Shark, Porpoise, Plaice, Bonito and - from September 1944 - Narwhal) were regularly broken, the associated Offizier keys were usually read when they carried any appreciable volume of traffic and a number of lesser keys were broken intermittently.

36. The three shifts were manned by Mahon, Noskwith and Joan Clarke, Pendered constituting a one man research section and taking a shift when one of the other three happened to be on leave. Mahon was primarily responsible for the successful breaking of the major keys being dealt with on watch; Pendered was responsible for all minor keys and if one of the major keys got into serious trouble and could no longer be dealt with currently (Porpoise for October 1944 is an example) this would be handed over to him for examination. This system worked very well; as a safeguard against the only real drawback to such a small staff - the danger of illness leaving insufficient people to manage the work - there was the possibility of getting back one or two ex-members should a serious crisis arise. [In fact one of the four (Joan Clarke) was away ill for six weeks and the remaining three managed for this period without outside help].


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