This Enigma machine is of the type used by the German Navy on
submarines to encode messages during World War II.
The machine is an electro-mechanical device that relies on a
series of ‘rotors’ to scramble plaintext messages into incoherent
ciphertext. Similar machines were first made in the early 20th
century, and the first ‘Enigma’ was invented by German engineer
Arthur Scherbius, who sought to sell it for commercial, rather than
military, purposes.
The Enigma was redesigned and improved several times in the
following years, and this particular machine was made in 1944. It
uses four code rotors and is housed in a wooden case. With it comes
a rare survival, a smaller case containing five interchangeable
spare rotors.
This naval-type machine is the most advanced Enigma machine
which was used in World War II, those used by the other military
forces only had three rotors, and two spares.
British Intelligence officers working at Bletchley Park near
London cracked the Enigma code, initially using methods developed
by Polish mathematicians. The messages sent out each day used a
different password, and discovering this password permitted the
messages to be read. The machines used in the decoding work were
called Bombes. They could only solve one problem, so were not
really true computers. The pioneering Colossus computers at
Bletchley Park were used to decode messages encoded by a different
machine, but decades of secrecy delayed the recognition of this
work.
The information received from deciphered material was codenamed
ULTRA, as the fact that messages could be deciphered had to be
closely guarded to prevent the encryption methods being
changed. This ability to decipher German military
communications is often thought to have helped bring the war to a
swifter end.