KRIEGSANSTEUERUNGSTONNE SWINEMUENDE was likely to go unaltered into the enigma version. The golden age of these cribs was the first half of 1942, by 1943 they were already falling off and eventually, by using dummy words and inversions, they ceased to be of any interest to us.
ii. Reencodements from Army and Air Cyphers.
There was surprisingly little reencodement between our traffic and that of Hut 6. The only reencodements to have occurred consistently over a long period were Mediterranean reconnaissance reports. These were usually easy to tie up and fairly difficult and amusing to attack; they had their heyday in early 1944 when Porpoise ceased to be breakable on its indicating system. These differed from all other reencodements in that they presented a problem of "translation": the German Air Force used very different cypher conventions, from the Navy so each message had to be turned into Naval language before it could be used. With a little practice this game could be played very successfully.
iii. Reencodements between Naval machine Cyphers.
Apart from those already mentioned all reencodements have been between keys we ourselves have broken and hence they only began fairly late in our history as the number of our keys increased. The most famous series of these reencodements were those originating in Shark and being repeated in Dolphin (later Narwhal) for the Arctic U Boats, Plaice for the Baltic U Boats, Turtle for the Mediterranean U Boats. These reencodements were messages of general interest to all U Boats - corrections to existing documents, descriptions of new Allied weapons, significant experiences of other boats etc. and they would start their career by being sent on all existing Shark services with often a note at the end ordering repetitions on other keys. Reencodements of this type were usually dead easy and, as they were usually long, one knew definitely when one had a right crib. A considerable time lag before reencoding - on Narwhal sometimes 3 or 4 days - often made identification difficult but had compensating advantages. Shark of the 2nd of a month might break Narwhal of the 4th and Narwhal of the 4th might also contain a reencodement of a Shark message of the 3rd. The 3rd Shark would break and its paired day the 4th would follow, providing perhaps a store of messages likely to appear in Narwhal of the 5th or 6th. Reencodements were fairly frequent, an overall average of perhaps 1 or 2 a day, and, with several keys involved, it was often possible to break all keys concerned for considerable periods on reencodements without having to use a single straight crib - a very economical process.