Having secrets and communicating them to others is as old as humanity itself. The trick was to find a way of transporting a message into a hostile environment. We have evidence that a favoured method was to shave the head of a slave, tattoo the message on the scalp and then wait for the hair to grow before dispatching the bearer of the message to wherever it was intended to go. There is an obvious disadvantage here, it can't be done quickly! You have to wait for the hair to grow again.
We don't know who first discovered 'invisible ink' but we know that by at least 600AD the Arabic nations knew that if a message was written using lemon juice it was invisible until the paper it was written on was exposed to heat. From then on different inks were tried, many of the experiments being conducted by the first scientists, the alchemists, who realised that an alternative way to make gold was to invent an undetectable secret ink. By the 16th century we find Mary Queen of Scots using invisible ink to communicate with her supporters on the continent in her plots to overthrow Queen Elizabeth. Sir Francis Walsingham, Elizabeth's spy-master, cracked this strategy, intercepted Mary's mail and eventually produced the evidence that took Mary to the scaffold at Fotheringay Castle on the 8th of February 1587.
In 1914 the German spy-masters faced the same problem as Mary, they needed a way of communicating secretly with their agents in Britain. Remember that wireless was in its infancy and the only route was by letters written to accommodation addresses in neutral countries. The surprising thing is that the first ink they turned to was the old stand-by, lemon or other fruit juice. As time progressed they used more and more sophisticated inks made from common objects. An aspirin dissolved in water made a good ink. A whole new field of research rose in Britain and Germany looking for new inks and ways of detecting them. Secret writing is still being used today, Al-Qaeda embed messages digitally in pornographic films distributed on the internet.
Man's ingenuity knows no bounds. From very early times cyphers and codes were used to conceal sensitive texts. The advent of the electric telegraph triggered a rash of commercial codes used by businesses for private communications. Governments invented their own codes and we all know the story of the cracking of the Ultra codes at Bletchley in WW2 and how important this was to the war effort. Similar codes are still being used today based on complicated mathematical algorithms. There was one strange secret writing method that is neither an ink or a code. In WW2 optical equipment was so good that it became possible to reduce quite large texts to a microdot which was concealed in text or under the stamp on a letter.
The only certain thing about this secret war is that eventually all the codes and secret writing methods will be cracked and new ones introduced!
Elizabeth with Lord Burleigh and Francis Walsingham.
