The History of Hut Eight

available. As cribs were good and 4 wheel bombes by now fairly plentiful we experienced very little difficulty for the time being.

Grampus still a 3 wheel key but no longer breakable by alphabets, fared less well. No one minded very much about Grampus and attempts to break June by cribs were rather unsuccessful. Research, however, revealed a reencodement from Henno, the Mediterranean reserve hand cypher, and at the end of June breaking got under way again. Between Juno 17th and August 12th most days were broken. At about this time the capture of Constanza killed the Henno reencodemont and Henno was abandoned; for a short time we attempted to hold on to Grampus with the help of weak cribs, but this proved expensive in bombe time and more or less barren of results and the key was officially abandoned. Soon afterwards we ceased to register traffic, though traffic from the Danube area was still being received until the end of the war.

With the abandoning by Bonito of the throw-on system in September this discredited procedure disappeared from the keys which we were breaking regularly and henceforth were entirely dependent on cribs. The throw-on system rendered Hut 8 unparalleled service compromising in the course of time Dolphin, Porpoise, Grampus, Bonito, Trumpeter, Sunfish and Seahorse. The Germans appear to have realised quite early the dangers of the system and in view of this were amazingly slow at eradicating it, in most cases they did not eradicate it until we knew enough about the traffic to continue breaking by cribs. The only merit of the system was that it reduced the number of messages that were undecypherable owing to corruption in the indicators; when the operator decodes the indicators he should get the same trigram appearing twice, if there is a difference he can try both possibilities.

In the middle of June the Americans captured the new bigram tables and Shark keys for June; Shark was therefore current for the rest of the month and other keys broke satisfactorily, Second Front notwithstanding. Most opportunely Lorient proceeded to produce an excellent crib for Dolphin at about 1400 hours, very soon after the daily key change, so that we were frequently current on Dolphin very early. On June 25th a special Stichwort on Dolphin was introduced for the Arctic U Boats only: this foreshadowed the introduction of Narwhal on September 1st, the Stichwort being intended to give added security until the new key was introduced. As the details of the Stichwort were announced in Offizier this gave us no trouble for the time being.

August passed without any new keys being introduced but with some deterioration in the security of the crib position. This was caused by the Germans in the South of France destroying their Dolphin keys. Rather curiously there had always been Dolphin


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