“Be secret and exult,” wrote William Butler Yeats in a phrase military men and warring nations would take to heart—as a current exhibit at the National Museum of American Historyin Washington, D. C., demonstrates. The exhibit—which is on display in the museum’s Computer Hall, fittingly enough—features cryptographic machines used during World War I and World War II. Recently declassified, most of the material is on loan from the National Security Agency.

Among the devices in the show is the German Enigma, used during World War II to send out thousands of ULTRA messages that the Nazis considered undecipherable by the Allies. Also on display is a rare photograph of the Bombe, an Allied machine used to break the Enigma’s code, together with one of the intercepted ULTRA messages. Other items include the U.S. M-134C, otherwise known as Sigaba, an electric cipher machine used for strategic exchanges between Winston Churchill and Franklin Roosevelt; a World War I Navy Cipher Box; and the U.S. Army’s M-94, a disk cipher patterned after a design conceived by Thomas Jefferson.

The exhibition will run through February of next year.