WHEN THE BOMBES eventually arrived at Bletchley
Park, significant inroads into the German army
and air force codes had already made. The Bombes,
however, enabled the Enigma settings to be
determined more easily, resulting in the decoding
process becoming much faster. The German navy
codes, however, presented greater difficulties to
be overcome.
An Enigma machine had been
recovered from U-33 early in the war. But the
Navy had already enforced strict security
practices and later added more rotors to their
system. Enigma now had eight rotors from which to
select the three actually used each day. Without
knowing the wiring of all the rotors, few
messages could be decoded. In May 1941 a German
weather ship, the Munchen, was boarded by the
Royal Navy, vital documents obtained and the ship
destroyed.
Soon afterwards the British Navy
captured and boarded the German submarine U-110.
Its coding equipment was intact.  Other
material recovered included codebooks, and key
listings for various German Navy and submarine
codes. The intact Enigma machine, with the daily
settings in place, together with its eight
rotors. The damaged U-boat eventually sank and
the crew taken to Britain and interned for the
duration of the war.
The 'mock-up' of a U-boat
section as used in the Mick Jagger film,
'Enigma', based on the story by Robert Harris.
(Right)
Admiral Doenitz, the commander of
the U-boat fleet, was, however, not convinced by
the assurances given to him concerning the
security of Enigma following the loss of U-110
and proceeded to change the set-up of U-boat
Enigma machines. This involved using four thinner
rotor wheels to fit into the space earlier
occupied by the three standard wheels. Although
Bletchley Park learned of the proposed change
from decrypts and other captured material, there
was little that could be done until the
alterations actually happened. It was indeed
fortunate that the other German forces continued,
in the main, to use the three rotor system.
For several months it looked as if
Bletchley was going to remain locked out from the
German naval codes. However, in October 1942 men
from the Royal Navy succeeded in capturing and
entering U-559 and recovered vital Enigma machine
parts and documents which allowed the code
breakers to get back into the German navy’s
codes.........
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