94 | 10 THE ENIGmA mACHINE
turned over a step whenever the right-hand wheel was in what was called a ‘turnover position’,
and the left-hand wheel turned forward whenever the middle wheel was in a turnover position.
Three turnover pawls controlled the motion of wheels. These were pivoted bars (situated at
the rear of the machine), with each wheel’s pawl engaging the toothed cogwheel mounted on
the side of the wheel. A wheel was in a turnover position whenever one of the turnover notches
on the wheel’s ring engaged with its pawl. The action of the pawl, the cogwheel, and the turn-
over notch combined to move the wheel forward a step.
Wheels I to V were at their turnover positions when the letters positioned at the top of the
wheel-rings (and visible through the viewing windows) were as follows:
Wheel I: Q Wheel II: E Wheel III: V Wheel IV: J Wheel V: Z
Wheels VI, VII, and VIII were a little different. Whereas each of wheels I to V had a single
notch, at a different place on each wheel, wheels VI, VII, and VIII had two notches each, at the
same places on each wheel. These three wheels were in their turnover positions when either M
or Z was positioned at the top of the ring.
Extra encryption
In so-called super-encryption a message (or indicator, or some other item) is encrypted multiple
times. Some especially important—or personal—naval messages were super-encrypted using
the Offizier system. First, an officer encrypted the message using an Enigma that he had set up
in accordance with the special ‘officers’ daily key’. Then the resulting ciphertext was encrypted
for a second time using the ordinary daily key. At Bletchley Park, these super-encrypted mes-
sages were called ‘offiziers’. Naturally, offiziers were especially difficult to break.
The officers’ daily key had the same wheel order and ring setting as the ordinary daily key,
but a different set of plugboard pairs was used, and there were only twenty-six permitted wheel-
starting positions. These were denoted by the twenty-six letters of the alphabet, and were valid
for a month. Each general key had its associated officers’ key. In the case of Dolphin, the officers’
key was known at Bletchley Park as ‘Oyster’.
Another example of super-encryption was the navy’s use of special codebooks for shortening
signals, as a precaution against shore-based high-frequency direction finding. The shorter the
radio transmission, the less chance interceptors had of determining its precise direction. These
special codebooks were employed, for example, to shorten reports of convoy sightings (using
the short signal book) and weather reports (using the weather short signal book). What would
nowadays be called a ‘compression procedure’ was applied.
Conclusions
The British wartime leader Winston Churchill said after the war:^12
The Battle of the Atlantic was the dominating factor all through the war. Never for one moment
could we forget that everything happening elsewhere, on land, at sea or in the air depended
ultimately on its outcome.