Battle Spy Codes of the Revolutionary War

While we were watching an episode of Liberty's Kids - The Complete Series (which, incidentally, my kids love with all their collective hearts) it mentioned how the mail was being intercepted during the Revolutionary War by both sides and that coding and other techniques were necessary in order to keep sensitive war communications secret.  The kids seemed really intrigued by the idea that Ben Franklin used invisible ink, so I ran with it.

First, I had the kids read this information article I found about the various spy techniques that both the British and the Americans were using during the Revolution.  We wrote our purpose (finding information about the different ways people sent coded messages) and then began annotating the article.  After a good first read (lead by me), then a second read in partners where the students wrote their own ideas about each technique, I had them summarize 3 of the most intriguing techniques, with evidence from the text in their summary.

We published using index cards. One card for each of the three most interesting spy techniques.

From there, we turned towards more math-y pursuits.  Since one of our math strands is working with order of operations, I combined that with creating a coded message.  The students wrote each letter of the alphabet vertically on a piece of paper.  They then created expressions containing at least one set of parentheses and two different operations.  It looked a bit like this:

A   (5 x 2) - 4
B   2(4 + 3)
C   15 - (2 x 3)

The students then solved each expression to make sure the answer was unique (no two letters could have the same end product).  This part is VERY challenging for the students.  It actually took them two days.  The process of thinking of problems, and then making sure they had unique values, really got their 5th grade brains moving!  Once all of the expressions were created, they did not reveal the expression answers on the final draft.  Those were turned in to me.  Their cipher key just had the letters and expressions.

The next step was to write a sentence that would be something that either the British or American sides would have wanted to encode.  The sentences needed to be at least 7 words long, but could convey any message within the theme.  They then drew the blank lines for each letter in the word, and put the number of the final expression answer underneath.  So it looked like this:

_____   _____    ______   ______   ______
  14          6             12            75           32

Finally, they created a finalized draft of the secret code on index cards, glued them onto envelopes, with the cipher key above it, and viola, there were 33 codes to be solved! 

I made copies of the codes and the students put them into their envelopes as well.  Now, whenever there is free time in class (after they finish their Calendar or Answer Is) the students can walk up and discover the secret codes that the American or British generals were sending.