Cryptographic History of Work on the German Naval Enigma

16. The other event in November was a very welcome visit from Captain (then Commander) Engstrom from Op. 20 G. The whole question of priorities on the American bombes was fully discussed and the decision was formally recorded that "It is agreed on principle that Air keys are considered on the same basis as Naval keys other than Shark. Decision between them to be based on current intelligence and operational value, but if value about equal Naval key to be given preference", a decision which was loyally adhered to throughout by Op. 20 G.


17. December saw a considerable recrudescence of interest in Sunfish by Naval Section and most of the month's traffic was read. The value of the traffic was less than had been hoped, because in addition to the main Sunfish key each blockade runner held a separate key of its own (the "Starfish" keys) and there was insufficient traffic normally to break these smaller keys. Unfortunately most of the important traffic was carried on the individual keys and Sunfish itself consisted largely of "family greetings". This idea of separate keys for separate units reappeared in November 1944 when "Sonderschluessel" were issued for individual U-boats and, later, for fortresses and individual flotillas. We were fortunate that the method was not developed sooner as few Sonder keys could be broken, because of the smallness of traffic and absence of cribs.

1944. January.

18. A new 3 wheel key, Plaice, carrying the Baltic traffic, started in January 1st. "Started" is not perhaps quite accurate as the East Baltic traffic had been on a separate key "Laube" for six months of the year when the East Baltic froze it rejoined Dolphin, presumably because there was then so little activity that a separate cypher was not thought worthwhile. The enemy now decided to put all Baltic traffic on the same key and to keep it separate for the whole year. Traffic started at about 150 messages a day and rose steadily throughout the year; on March 13th 1945 when the Russian advance was in full progress 805 Plaice messages were sent.


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