Revolutionary War Codes and Invisible Ink

What's a war unit without a discussion of spies and military intelligence? There are so many great little details about spying in the Revolutionary War, too---like the spy that got caught, swallowed a tiny little silver capsule containing the evidence, was given ipecac to force him to throw up the capsule, swallowed the capsule again, and was forced to vomit again. The Patriots finally got that secret message! The children loved that story.

We read the book George Washington, Spymaster, which was full of great stories like that, and makes a convincing case that it was military intelligence that really won the war for the Americans. Fascinating.

Here's another article on the subject, from Scientific American.

We did a bunch of fun spy-related activities. First, of course, we wrote messages in invisible ink (lemon juice + a little water). We wanted to be authentic, so (living dangerously!) we decoded these messages by holding them over a candle flame. 

Once they'd tried their hands at writing messages themselves, I set up a little treasure hunt for the children, using several different kinds of code used in Revolutionary War times. 

To be even trickier, I wrote decoy information on my invisible-ink messages, so if the paper got into the wrong hands, it would look like a simple shopping list or note to a friend.

Only when held to the flame would the true message be revealed! (Of course, when you decode your message over a flame, you run the risk of burning off part of your message . . . a problem I'm sure the Revolutionary War spies ran into as well! Luckily the essential message here could still be read.)

Another coded message I made for the treasure hunt used the "mask" technique, which is one of my favorites. You use a pre-cut "mask" over the paper (simply a cut-out shape, like a stencil) to write the substance of your message. The one receiving the message has the same mask to use for decoding. 

Once the true code is written, you fill up the rest of the paper with unimportant or misleading information (it's quite fun trying to find sentences that flow smoothly into your secret message, while obscuring its meaning!), leaving the secret message hidden in plain sight! With the mask removed, this looks like an innocent letter full of trivialities. No one will suspect a thing! :)

After the children successfully completed the treasure hunt (it led to a hidden cache of provisions for the soldiers!), we talked about sealing wax, insignias, and signets, and how those could prove (or obscure) the authenticity and secrecy of a document. I know you can buy actual sealing wax, but I didn't have any, so we just dripped candle wax onto our letters to seal them. Then we imprinted our "seals" into the wax. It was really fun!

I considered making berry ink again and writing with quill pens as we did for our Civil War Unit, but we didn't get to it this time. That activity would go well with this lesson too, though!