An early method for decoding Enigma messages was basically a paper method involving representing
the Enigma wheels by strips of paper or card. Turing called
these "comic strips". A colour coding was used to identify the
Enigma wheels and this is used here.
The "Set Wheels and Steckers" must be clicked before starting.
A background sheet of paper has printed on it vertical strips of
letters. On the left hand side is the
representation of the Umkehrwalze (reflector), U.K.W. This
contains two columns. The right hand of these is the entry
and exit terminals, just the alphabet repeated. The left hand
column contains the connection within the U.K.W. For
instance the entry terminal A is connected to the Y terminal.
The column of letters on the background sheet on the right
hand side represent the Stecker, (plugboard) connections.
This column is overwritten with the Steckers entered into the
Steckers text box.
The wheel strips contain a lower case alphabet on the right hand side,
an upper case alphabet down the centre and the
wheel wiring in lower case in the left hand column. The letter entered into
this column is the letter to which it is connected on the right
The upper case alphabet down the centre represents the Ringstellung or
tyre setting on the wheel. It is placed so that the Ringstellung
letter on this strip is alongside the letter Z in the left hand
column of the wheel. For instance on wheel IV in this
example, its Ringstellung is G so G on the Ringstellung strip
is alongside z. The coloured strips and lower case letters represent the core cross
wiring inside the wheel. The upper case alphabet strip represents the tyre
ring and its letters. It is these letters which show through
the windows on the Enigma machine.
In the default example, wheel IV (4) is on the left, wheel II (2),
in the centre and wheel V (5) on the right. The rings are set to
G on the left, M in the centre and Y on the right hand wheel. The
wheel start positions have been set to DHP and these appears lined
up with the Z* and *Z* on the background sheet. (use the vertical
scrollbar to bring these to the centre of the screen).
This is the same as turning the wheels on a real
Enigma until DHO shows in the windows. This is the indicator
setting for decoding the message setting. This on the
intercepted message is GXS. The strip for the right hand wheel, V,
has been moved up one place to P. This is because the current flows
through the real Enigma and lights a lamp AFTER the right
hand wheel has moved due to the entry key being pressed
So now it is possible to decipher G, the first letter of the
message setting. Entering on the far right hand side at G
leads to i on the right hand side of wheel V. (taking into
account that G is Steckered to R). Now finding i on the left
hand column of wheel V leads to y on the right hand
column of the middle wheel II. Finding y on the left hand side
leads to t leading to q in the right
hand side of wheel IV and q on the left hand
side leads to Q on the Umkehrwalze. This leads to E on the
output of the Umkehrwalze leading to z on the left hand side of
the left hand wheel. Finding z on the right hand side leads to i
on the left hand side of the middle wheel. Finding i on right
hand side leads to G and on the real Enigma, the G lamp would light.
The right hand wheel V is now moved up one position by changing the
right hand letter in the wheels start box to Q and clicking on Set Wheels
and Steckers. Now the next entry of X can be made. When this is
traced through it returns to L so the L lamp would have lit.
Changing the right hand wheel to R allows S to be entered.
This comes back to P and the P lamp would have lit.
Thus the enciphered message setting, GXS deciphers as