The History of Hut Eight

lated from the Archery assuming linear latitude and longitude tables for the 2nd and 3rd letters of the first group. A probable solution for a fifth message was found.

On the basis of three certain decodes with Archery to go with them, Tables 1 and 2 were constructed and 4, 5, 7, 8, identified as being identical with the equivalent tables in the old addition. The same assumption was made about Table 6 which was identical in some places with the old (doud?) table but was in fact different in others.

Reading for pressure change characteristic and swell (and sometimes for past weather) had appeared in Archery after Jan. 20th, and it was assumed that Tables 3 and 9 were associated with these, or with the 1st letter that might be an indicator (or might not). Dolphin WWs did not exist until June, but two more Shark WWs were decoded on the two days broken in Feb. and after this, a first and almost correct attempt was made to reconstruct Table 9.

In May the trigrams disappeared from WWs altogether, and it was assumed that the first letter must be an indicator as before. (The trigrams were later shown to be discriminants). In June Norwegian land stations started to send WWs in Dolphin. There was no Archery but the latitude and longitude were fixed and WWs were easily rodded. There were 45 Dolphin WWs between June 24 and Nov. 22 and all but three were decoded. By October Tables 9 and 3 were constructed correctly and the Time basis of the Indicating system understood. The number of indicator equivalents known was insufficient to make any attempt to break Shark on WWs possible: this had to wait until the capture of U 559 gave us complete Indicator tables for the first time. The reconstructed table WEIMAR went out of force on Oct. 25th.

DECEMBER 1942 - MARCH 1943:

The capture of the complete indicator tables and codebook for WWs was of vital importance and enabled WWs to be used for breaking Shark operationally. The method was used with success till March 10th when the 3rd Edition of the WW book came into force. During the period, 88 out of 99 Shark days were broken - all on WWs.

Between 1 and 3 all wheel order menus were required to break the first day of each pair. The speed, however, with which a menu could be obtained depended on how soon Archery could be supplied by the Met Section. No set of trigram substitution tables was recovered sufficiently for use until the 4th or 5th day of its first 6-day life, so that when Norddeich used new tables, the speed of breaking Shark went down. As was stated


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