The original of this document is held in the United Kingdom at the National Archives, Kew, Richmond, Surrey, TW9 4DU. Reference HW 25/2.


1939 - 1945


A. P. Mahon

The king hath note of all that they intend,
By interception which they dream not of.

King Henry V.



1. The Machine and the Traffic.

2. Ancient History. The Research Period.

a. Early work on Enigma.

b. Digression on Banburismus.

c. January 1940 to July 1941.

3. Digression on Bombes.

4. Cribbing.

a. The beginning of the Crib room.

b. Depth Cribbing.

c. Straight Cribs.

d. Reencodements.

5. The Beginning of the Operational Period.

Including discussion of Emergency procedures and Offizier keys.

6. Porpoise.

7. Shark and 4 Wheel Bombes.

8. Short Signals.

9. Shark after the End of the Short Signal Period.

4 Wheel Bombe Policy and the contribution of OP 20 G.

10. Other Developments during 1943.


Sunfish and Starfish.

The Abandonment of Banburismus.

11. 1944 - 1945.

Developments month by month and digressions on

Wheel Order Rules and the problem of the multiple

Grundstellung and changing bigram tables.

12. The End.

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