Royal Signals Museum - Early Codes

The Alphabet & Saw Tooth Codes

Some of the early codes that were used by the Army were easy to operate.  Unfortunately, they were also easy for the enemy to crack.  The following are some of these early codes. Try them they are great fun.  See if you can use them AND crack them.

ALPHABET PAIRS

In the ALPHABET PAIRS Code the letters of the alphabet are listed in pairs as shown below. This can be done at random. Numbers can also be included.

The coded message is produced by substituting the original letter with its partner:

A becomes N. 1 becomes 6. Z becomes M. And so on.

Message: MOVE AT 1000 HOURS Becomes coded Message ZBIR NG 6555 UBHEF.

Now try decoding this message:  BHE ZVFFVBA VF GB PNCGHER GUR UVYY.

Try arranging a new list of alphabet pairs on a piece of paper and then send and receive messages with a friend. 

SAW TOOTH CODE

It is easy to see how the saw-tooth coding system got its name. First, the message to be coded is written out with alternate letters on upper and lower lines. The effect is to make it look like the teeth of a saw:

THERE IS NO AMMUNITION LEFT FOR THE RIFLES

Then the top line is written followed by the bottom line to provide the coded message:

TEESOMUIINETOTEILSHRINAMNTOLFFRHRFEX.

Now try decoding the above message by doing the reverse. First, divide into 2 equal halves.  Second, put the second half under the first.  Third. write down the decoded message by taking alternate letters from the upper and lower lines - start with the upper line first.  Can you see why there is an X at the end of the coded message?

Now see if you can decode this message:

TEOASGASABDESNWAJMYYHSLIRHRYLINLCPAGIKONSIMBTEODES.

Try making a coded message using the saw-tooth code and ask a friend to decode it.