Wheel Starts

Set Wheels and Steckers
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 hand column.

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 down.

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 RLP.