parts of the January Red and March Mustard keys, with the remainders being used to make up the April Red key-list. In June, Locust, Mosquito, Snowdrop, Hornet and Garlic also consisted of partial key repeats. Key repeats died out at the end of 1942, but were briefly revived between March and June 1943, when ciphers used by certain
Luftgau
(
Luftwaffe
administrative units) were allotted different discriminants, but some key components were identical, for example, Daffodil, Gorse, Lily and Speedwell formed one group.
Primrose, the cipher for
Luftgau
XXVIII, the
Luftwaffe
supply unit in Africa, yielded between 140 and 290 decrypts daily, mainly on logistics, on most days between June and November 1942 – almost as many decrypts as the prolific Red, whose total varied from 350 to 445 daily. Primrose was doubly useful since it also provided complete key repeats, although in random order, for Scorpion (employed by
Luftwaffe
close support units and
Luftwaffe
liaison officers with the Afrika Korps) for each month from June to November. Scorpion was very difficult to intercept in Britain, since it was transmitted with low power on medium frequencies by units near the fighting. Special arrangements were made to decipher it at Heliopolis, near Cairo, as well as at GC&CS, since it produced a great deal of intelligence about
Luftwaffe
plans and the ground fighting. The daily keys were available in advance so that messages in it could therefore be deciphered immediately they reached the Heliopolis centre.
In complete contrast to the
Luftwaffe
,
Heer
traffic in 1941 was divided into small, unrelated groups, with few re-encipherments, and light traffic. Hut 6 broke very little
Heer
Enigma before September 1941. Thus, although Vulture (used on the Russian front) was first read on 27 June 1941, shortly after the invasion of Russia, Hut 6 broke no Vulture keys for August, and only one for September. It solved only twelve
Heer
daily keys in August, all in Kestrel. By November Hut 6 was breaking both Vulture, which was the first
Heer
cipher to be broken regularly, and Chaffinch, but then lost them for four months after the Vulture traffic was reduced when the
Heer
began to rely more on land lines.
Heer
ciphers in North Africa were initially very difficult to solve. Hut 6 broke Chaffinch II (used between
Panzerarmee
Afrika and Rome and Berlin) for nine days in September 1941, and for part of October and from 2 November to 6 December, although often a week or more later. Traffic on Phoenix, which rose from twenty-five to over 200 messages daily during fighting in Libya, could only be taken by forward intercept sets with the 8th Army, since it was also transmitted at low power on medium frequencies. When it was broken, delays in sending the traffic back from 8th Army to Heliopolis for transmission to GC&CS led to considerable hold-ups, until arrangements were made for Hut 6 to send key-lists to Heliopolis. Hut 6’s solution of the
Heer
Mediterranean ciphers, such as Chaffinch, Phoenix and Thrush (which carried information about the air transport of supplies and reinforcements) increased considerably after April 1942. Even so, only 2,800
Heer
signals were decrypted in May 1942 out of 10,300
Heer
intercepts, compared with 19,400
Luftwaffe
decrypts from 31,000 intercepts, illustrating just how difficult it was to solve
Heer
Enigma.
Hut 6 found that many of the twenty-two
Luftwaffe
ciphers it was regularly breaking by the summer of 1942 were interrelated: the fifty
Heer
and
Luftwaffe
Enigma ciphers then being used presented it with a single, indivisible problem. It therefore had to try to break every single cipher, however unimportant for intelligence purposes, since there was no way of telling in advance which would prove the entry point to a different cipher. Even
Heer
Mediterranean ciphers, such as Mallard (a Rome administrative cipher), were sometimes broken by re-encipherments from Red and Scorpion. All the Mediterranean
Heer
keys solved in
Luftgau
(
Luftwaffe
administrative units) were allotted different discriminants, but some key components were identical, for example, Daffodil, Gorse, Lily and Speedwell formed one group.
Primrose, the cipher for
Luftgau
XXVIII, the
Luftwaffe
supply unit in Africa, yielded between 140 and 290 decrypts daily, mainly on logistics, on most days between June and November 1942 – almost as many decrypts as the prolific Red, whose total varied from 350 to 445 daily. Primrose was doubly useful since it also provided complete key repeats, although in random order, for Scorpion (employed by
Luftwaffe
close support units and
Luftwaffe
liaison officers with the Afrika Korps) for each month from June to November. Scorpion was very difficult to intercept in Britain, since it was transmitted with low power on medium frequencies by units near the fighting. Special arrangements were made to decipher it at Heliopolis, near Cairo, as well as at GC&CS, since it produced a great deal of intelligence about
Luftwaffe
plans and the ground fighting. The daily keys were available in advance so that messages in it could therefore be deciphered immediately they reached the Heliopolis centre.
In complete contrast to the
Luftwaffe
,
Heer
traffic in 1941 was divided into small, unrelated groups, with few re-encipherments, and light traffic. Hut 6 broke very little
Heer
Enigma before September 1941. Thus, although Vulture (used on the Russian front) was first read on 27 June 1941, shortly after the invasion of Russia, Hut 6 broke no Vulture keys for August, and only one for September. It solved only twelve
Heer
daily keys in August, all in Kestrel. By November Hut 6 was breaking both Vulture, which was the first
Heer
cipher to be broken regularly, and Chaffinch, but then lost them for four months after the Vulture traffic was reduced when the
Heer
began to rely more on land lines.
Heer
ciphers in North Africa were initially very difficult to solve. Hut 6 broke Chaffinch II (used between
Panzerarmee
Afrika and Rome and Berlin) for nine days in September 1941, and for part of October and from 2 November to 6 December, although often a week or more later. Traffic on Phoenix, which rose from twenty-five to over 200 messages daily during fighting in Libya, could only be taken by forward intercept sets with the 8th Army, since it was also transmitted at low power on medium frequencies. When it was broken, delays in sending the traffic back from 8th Army to Heliopolis for transmission to GC&CS led to considerable hold-ups, until arrangements were made for Hut 6 to send key-lists to Heliopolis. Hut 6’s solution of the
Heer
Mediterranean ciphers, such as Chaffinch, Phoenix and Thrush (which carried information about the air transport of supplies and reinforcements) increased considerably after April 1942. Even so, only 2,800
Heer
signals were decrypted in May 1942 out of 10,300
Heer
intercepts, compared with 19,400
Luftwaffe
decrypts from 31,000 intercepts, illustrating just how difficult it was to solve
Heer
Enigma.
Hut 6 found that many of the twenty-two
Luftwaffe
ciphers it was regularly breaking by the summer of 1942 were interrelated: the fifty
Heer
and
Luftwaffe
Enigma ciphers then being used presented it with a single, indivisible problem. It therefore had to try to break every single cipher, however unimportant for intelligence purposes, since there was no way of telling in advance which would prove the entry point to a different cipher. Even
Heer
Mediterranean ciphers, such as Mallard (a Rome administrative cipher), were sometimes broken by re-encipherments from Red and Scorpion. All the Mediterranean
Heer
keys solved in
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