HAGELIN CD-57 

Mechanically operated pocket cipher machine in two-part military case variant (5½ x 3 in.) of drab-green die-cast aluminum, serial number 3003993, complete with 6 coding wheels (29, 31, 37, 41, 43, & 47) and rewinding crank housed in case lid. Hinged top lid with case lock, white on black input/output letter disk, crank insertion hole, and window revealing letter counter, case bottom with cipher tape holder, operating lever, and locking lever, the whole opening to reveal keying mechanism with input/output disc, and stack of 6 coding wheels on axle with drum locking lever. 

A FULLY FUNCTIONAL HAGELIN CD-57 POCKET CIPHER DEVICE. Developed by Boris Hagelin in 1957, the eponymous Hagelin CD-57 was a mechanically operated, pin-and-lug pocket cipher machine that remained in service until the mid 1970s. By secret arrangement with the United States National Security Agency, two primary versions of this device were made; the CD-57, made for use by NATO and NATO-friendly countries, and the CD-55, made for use by non-NATO countries. The two appeared identical, however the CD-55 was much easier to break; the CD-57, basically a pocket-version of Hagelin's unbreakable CX-52 desktop cipher machine, featured a highly improved stepping mechanism and could quickly be converted to an unbreakable one-time tape (OTT) cipher machine by replacing the 6-wheel stack with the so-called RT/CD (Random Tape) option and fitting the bottom of the case with a key tape cassette.

Because of its easily concealable size, the CD-57 was popular with a number of intelligence agencies during the cold War, as well as with many European and other armies.