Children love the idea of being able to write a message in code that no one but them can understand -  where they will meet, what games they will play or where that secret stash of Pokemon cards has been hidden – the subjects for codes are many and varied, and can really be anything that requires a degree of secrecy and mystery. 

The basic concept of writing in code relies on being able to assign a predictable symbol to each letter of the alphabet, based on a set of rules that are known to the sender and the receiver of the code. 

The simplest of codes uses the substitution of one letter of the alphabet for a different letter using a rule which is applied and known by the message sender and recipient. 

Codes can have their serious side too, though. 

Codes have been used throughout history as a way of sharing military information such as the movement of equipment or troops or plans for managing attacking and defensive strategies in a war situation. 

They are also used as a way of sharing messages across long distances in situations where written text is impractical. 

The ability to decipher a code requires a good knowledge of the construction of English language and also the ability to apply that knowledge mathematically to work out a rule which can be applied to the code to solve it.

Julius Caesar

Julius Caesar, the Roman military leader and writer who lived in the period around 100 BCE to 44BCE, was believed to be an early user of a simple code system. 

Known as the Caesar cipher, the code relies on a simple replacement of letters by shifting them three places to the left. 

In this way, Caesar was able to communicate messages of military significance to his generals without them being able to be read by his enemies. 

The term ‘Caesar cipher’ is still used today to refer to a letter shift system of coding.

Students can experiment with this technique by making two alphabet strips and placing one directly above the other on their table.

The last three letters one the right hand end of one strip are cut and moved to the left hand end and taped in place, and then the strips can be aligned on the table one above the other to create a three letter shift.

To write in code, it is a simple matter of reading the ‘code’ letter on bottom strip which corresponds with the chosen letter on the top strip.

Once students have mastered using the traditional Caesar three letter shift method, they can experiment with creating other rules using the same approach and seeing whether other students can work out a technique to help them crack the code. 

Morse Code

Morse is another method of transmitting text using a code, and is named for the telegraph inventor Samuel Morse.

A message is coded using a series of dots and dashes, where each letter of the alphabet has its own dedicated pattern. Spaces are left between words so that the receiver can work out where one word ends and the next begins.

Morse was used frequently by radio operators and in aviation and maritime settings, but has been replaced by other methods over recent years.

The international symbol for distress, SOS, is still recognised around the world by the morse code …- - -… (dot, dot, dot, dash, dash, dash, dot, dot, dot).

Morse code was important in the late 1800s when it was possible to transmit the code before voice was able to be transmitted by radio, and it was also critical during World War Two when it helped transmit messages between warships out at sea and to assist pilots to identify navigational markers which transmitted two or three digit signals which could be matched to navigational charts.

Students can practise their skills at transmitting morse code by using a torch and flicking the switch on and off to share a message.

The receiver of the message will need a morse code alphabet (available online) so they can ‘read’ each letter of the message and write down what is being sent as code.

Sending a morse code message can be challenging and time consuming for a beginner, and it is easy for a message to become lost in transmission if an error is made.

For this reason, suggest that students use a very short message or experiment initially with transmitting single words rather than whole sentences.

Another technique that can work well is to show students how they can press an object such as a soft pencil tip (for a dot) or a paper clip (for a dash) into a strip of playdough which has been flattened onto the table, creating dots or dashes which can then be read by the receiver. 

Enigma Machines

During World War Two, much of the communication of the Germans was done using a complex device called an Enigma Machine.

This machine employed a system of three rotor wheels which were turned to create a complex code that was extremely challenging to crack.

At a place called Bletchely Park in England, many code breakers worked hard to try and decipher the code that was used within the Enigma Machines that governed much of the German communications.

Their work was helped by the capture of an intact enigma machine from a German U boat in May 1941, which allowed the British to eventually decipher German communications.

Many historians believe that the fact that the code transmitted by the Enigma machine was able to be deciphered without the Germans realising it had been cracked was a significant factor which changed the tide of the war.

Many of the code breakers who worked at Bletcheley Park had one key feature in common – they were lovers of crossword puzzles, and particularly good at cracking cryptic crosswords.

Some of them were recruited after responding to a challenge issued by The Telegraph newspaper which ran a competition in 1942 to see if anyone could crack a challenge crossword printed in the paper in less than 12 minutes.

Some of the winners of the competition were then offered work at Bletcheley Park cracking military codes.

Older students will enjoy the movie The Imitation Game which explores the life of Alan Turing, a brilliant mathematician who worked at Beltchley Park, attempting to crack the Enigma Machine codes during the war.

This fairly lengthy film has a PG rating and can also be used as a discussion prompt for topics such as how film makers depict historical events the way Turing’s personal life is shown in the film.

Students may also complete inquiry based learning tasks about code breaking during the war or test their own skills at crosswords using the quick crosswords or cryptic crosswords in the newspaper or online.

Learning about codes and how to write or crack them can be explored with students across a range of levels and ages, inviting them to apply their research skills as well as their mathematical and linguistic knowledge to the challenges of sharing a message that can only be understood by the sender and the recipient.

Can your students crack the code?