Enigma machines at the National Cryptologic Museum.

Seven Enigma machines are shown, from left to right (placard text in italics, if known):

Left display: Enigma machines 1923–1939.

• Commercial ENIGMA. This machine, marked in English "Made in Germany" was intended for commercial export. Such Enigmas were available to anyone who wished to purchase them prior to the Nazi takover of the German government.
• "T" ENIGMA. A commercial type machine specially wired. Five hundred of these Enigmas were given to the Japanese Navy for joint communications.
• "G" ENIGMA. A specially constructed machine supplied to some foreign governments friendly to Germany. Two hundred "G" Enigmas are known to have been issued to the German High Command (OKW) for an unknown "special purpose".
• To...to ENIGMA...encryption...The use of te...this added 150...The preselected ch...STECKER combinat...wiring, made them...ENIGMA's security and t...machine.

Right display: Enigma machines 1939–1945

• DIE LUFTWAFFE (AIR FORCE). Like the Army, the German Air Force relied on the Enigma for communications security. As a result of radio intercept and timely cryptanalysis, which was aided by poor COMSEC on German radio nets, plans such as those for the decisive air attacks known as the "Battle for Britain" were revealed to the British well in advanced of the intended strike. The losses suffered by the German Air Force during this time were never regained.
• DAS HEER (ARMY).

The three rotor Enigma became the cryptologic workhorse of the German land forces before World War II and continued as such until V-E Day. Rugged, completely portable, and requiring no external power source, the machine was ideally suited to the highly mobile "lightening" type of war envisioned and practiced by the German High Command. Although a few German officers felt that Enigma could be broken by a determined cryptanalytic attack, the prevailing feeling was that the time needed by a cryptanalyst was so great that its value would be lost-no serious effort was made to determine otherwise.

• Enigma Uhr. The "Uhr" (clock) was a mechanical device used by the German armed forces in World War II to further increase the security of the Enigma. When the clock plugs were substituted for the original ones in the Enigma plugboard, the electrical current was directed through the clock. By simply turning the large knob on the clock, the Enigma operator could select 40 different plugging arrangements without actually rearranging the plugs!
• DIE KRIEGSMARINE (NAVY). With a naval force small in numbers, but technically advanced, the German Naval High Command, in order to offset Allied numerical superiority, adopted a strategy designed to conceal as much as possible the location, intention, and movement of its forces. Forced by its nature to rely on radio communications, the German Navy issued to each vessel from battleship to harbor defense craft an Enigma cipher machine to ensure security. Here as with other services, the dependence upon Enigma for communications security proved to be disastrous.