For Gustavus Selenus, as well as for later seventeenth-century political activists and Royal Society members John Wilkins, John Wallis, and Samuel Morland, cryptography was at once a communicational necessity during the Wars of the Three Kingdoms and their aftermath and a playful personal game of wits. Selenus, Wilkins, and Morland, along with Noah Bridges and John Falconer, authored instructional manuals to share their methods for creating unbreakable messages and deciphering complex, polyalphabetic, and even multimodal ciphers, and they were motivated by political and military advancement as well as individual academic curiosity and a love of mental challenge. Wallis's papers, edited by John Davys in 1737 as An Essay on the Art of Decyphering, characterize the genre's approach to cryptography with the term vaga Venatio (‘rambling hunt’): ‘[W]e sometimes start the Game, where we little expected to find it; but when that is once done, we are sufficiently recompenc’d by the Pleasure we take in the Pursuit.’ These print handbooks, which sold enough copies to warrant multiple editions, help everyday readers protect national and personal security as citizen-spies by promoting cryptography as an intellectually pleasurable game.

The importance of cryptography to military success may be intuitive for twentyfirst- century readers; since World War I and the publicized, well-documented roles of intelligence organizations like the Military Intelligence Division (MID), Bletchley Park, and organizations like the National Security Agency (NSA), ciphering and deciphering have become accepted necessities for national security. Countless histories report the ways in which modern wars have pivoted upon secret communication and the sophistication of a nation's military cryptography capabilities.