pursuits) there was a crib room and a research crib room. When traffic began to be teleprinted a separate registration room (R.R.) was set up and as bombes became more plentiful a separate bombe testing room was necessary - the machine room (M.R.). Decoding* for some time was done by the Hut 6 decoders (regular breaking began about a year earlier in Hut 6 than in Hut 8 so there was a substantial Hut 6 decoding section in existence before we had any similar organization), then it was done as a part time job by "Big Room" typists and finally a separate D.R. (administratively part of the Big Room, but otherwise independent) was set up. We therefore had ultimately four rooms replacing the old Big Room - M.R. (bombe testing), R.R. (registration), D.R. (decoding), Big Room (all other clerical work).
4. The best way to get a general picture of how things worked is to trace the progress of traffic through the hut, taking a period in Summer 1943 when we were installed in Block D but had not yet given up Banburismus. (1) The traffic was teleprinted from Scarborough and two copies (three in cases when a copy was sent to Washington) sent by conveyer belt to the R.R. (2) An R.R. girl examined the message to see whether it was Mediterranean traffic, (Porpoise, and later Grampus, in which case the indicators throw-on), or "K booking" traffic (Dolphin or Shark, using the K book and bigram tables). The method of registration being different in the two cases the traffic separated at this point into these two groups which were handled by different people; Mediterranean being headed "Nile" and the remainder "Nuts" there was no difficulty in separating them. Let us suppose the message we are tracing through was on Dolphin and that the day's traffic was going to be Banburized. (3) The message (second copy still attached) then had first and last group recorded; this process discovered whether or not it was a "dupe" (duplicate of message already received). If it was a dupe, it was recorded on the register and attached to its original. If it was not a dupe, it was numbered, bigrammed and K booked i.e. the bigram substitution was made
*Decyphering is the correct term but we invariably spoke of decoding and the Decoding Room and I shall use this term here.