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A model of the Jefferson Wheel Cipher created by Ronald KirbyA model of the Jefferson Wheel Cipher created by Ronald Kirby

While serving as George Washington's secretary of state (1790-1793), Thomas Jefferson devised an ingenious and secure method to encode and decode messages: the wheel cipher. During the American Revolution, Jefferson had relied primarily on messengers to hand-carry sensitive letters. When he became America's minister to France (1784-1789), however, the adoption of codes was necessary. Codes were an essential part of his correspondence because European postmasters routinely opened and read all diplomatic and any suspect letters passing through their command.

As described (though perhaps never built) Jefferson's wheel cipher consisted of thirty-six cylindrical wooden pieces, each threaded onto an iron spindle. The letters of the alphabet were inscribed on the edge of each wheel in a random order. Turning these wheels, words could be scrambled and unscrambled.

A model of the Jefferson Wheel Cipher with its first four disks removed and laying sideways below
A model of the Jefferson Wheel Cipher with its first four disks removed and laying sideways below

As an example, the sender of the message shown in the picture, "COOL JEFFERSON WHEEL CIPHER," spells the message out and then looks to any other line of text – possibly the one directly above, which on this version of the cipher begins with the letter "N." The sender then copies the rest of the letters from that line into the correspondence to spell out "NKYG NSUS NXML CQYO TYUH HFTD."

The recipient of the coded message would spell out these random-seeming letters on his own identical cipher and then begin looking for the one line that made sense. In this case, the line below.

Although Jefferson seems never to have used the wheel cipher, and apparently abandoned the idea after 1802, it was independently "re-invented" in the early 20th century. Designated as M-94, it was used by the Army and other military services from 1922 to the beginning of World War II.  A short time later, Jefferson's design was found among his papers.

The cipher shown is a reproduction made according to Jefferson's instructions, with the exception that it has only 24 wheels instead of 36. The model is presently part of Monticello's education collection.  Another model, created by scholar Silvio Bedini, is in the collection at the National Museum of American History in Washington, D.C. Functioning adaptations are available for sale in Monticello's Online Shop.

- Ann M. Lucas, 9/95; revisions by Chad Wollerton, 12/03 and 4/05; revised by Anna Berkes, 6/4/15; revised by Chad Wollerton 2/13/17

Further Sources