9. As well as working on Shark they attacked various other keys (Turtle, Pike, Sunfish and Seahorse) their best result being on Seahorse the key used by the German Naval Attache in Tokio; as a key with Japanese connections they had a particular interest in it and after the initial break was made here they had a number of successes ultimately reading most of the 1944/45 traffic. In addition of course to work on the keys they handled cryptographically themselves they ran large number of cribs on other keys sent to them by us.
10. Another important contribution was on wheel order rules; they discovered a number of restrictions which resulted in the saving of a very considerable amount of bombe time [See Chap VI]. They also helped a great deal in breaking Offizier settings - indeed after a bit we began to think that perhaps it was we who were occasionally helping them rather than the other way round!
11. We always had very satisfactory relations with our opposite numbers, in particular with Capt. Engstrom (head of all machine development) Lt. Cdr. Church (head of the Op. 20 "Hut 8") and Lts. Eachus, Clifford and Pendergrass, U.S.N. liaison officers with us at different times and I would like to express our warm appreciation of all they did.
The History of the Later Period.
12. The nature of the history from now on is rather different. Up till now we have had a few keys but a considerable amount of cryptographic development to describe. From now on we shall have many more keys but fewer purely cryptographic innovations. The difficulties in the later period are chiefly those arising from increasing size and complexity - one notable exception to this being the multigrundstellung problem which arose in the last months of the war. The history therefore contains more incident but fewer landmarks and is harder to present in a clearcut pattern; the various graphs included in the appendices give a better general idea of the course of events than a written survey. The account of the last two years will inevitably be very much of patchwork; it will be given in