FORT MEADE, Md. — Nicknamed American Dragon, the cryptologic device was constructed by the Signal Security Agency (SSA) in 1944 to assist the British Colossus — a set of computers created by British codebreakers largely to break the German’s Schlusselzusatz SZ-40 Cipher machine.
“The American Dragon machine is believed to be the only existing rapid analytic machine from WWII,” said Spencer Allenbaugh, the collections manager for the NCM. “To have an artifact like this, still in great condition, is a great find and piece of history for the National Cryptologic Museum.”
The SZ40, code-named “Tunny” by the British, was Germany’s teleprinter cipher attachment. The SZ40 enciphered and deciphered the German High Command’s messages, many of which were signed “Adolf Hitler, Führer,” to army commands throughout occupied Europe.
Arriving at Britain’s Government Code and Cipher School (GCCS) in Bletchley Park on 14 October, 1944, the American Dragon was quickly appreciated. Just four days after its arrival, GCCS was requesting additional Dragon machines to assist in their operations. However, SSA had decided early on that only one prototype would be built by the U.S., and Britain would have to build more if they needed them.
On 1 November, 1944, the GCCS reportedly began to build its own dragon machines. While initial use of the American Dragon proved successful, it was never utilized completely. SZ40 intercept traffic was limited, and generally the Colossus handled the bulk of the work.
The American Dragon was used on high traffic days until the British Dragon was completed on 4 January 1945. At this point, the GCCS concluded that the British Dragon was more reliable and the American Dragon was most likely retired.
The SZ40 utilized rotor wheels to generate a key stream to encipher plaintext messages. The enciphered message would then be transmitted to the receiving SZ40-attached teleprinter, which would decipher the message. There were 12 rotor wheels on the SZ40 broken down into five regular stepping wheels — termed the chi wheels, five irregularly stepping wheels —termed the psi wheels, and two motor wheels.
The Colossus could solve the settings on these SZ40 wheels thereby breaking the key stream, but the process took time. When there was a high amount of intercept traffic coming through, the American Dragon was used to find the psi settings through crib dragging — the testing of known or presumed parts of an encoded message.
In this case, the Colossus would solve the chi wheel settings and then the Dragon would use this data to solve the psi wheel settings. The Dragon’s help enabled the Colossus to move to another intercepted message.
Bletchley Park returned the American Dragon to the SSA at Arlington Hall in Virginia at the conclusion of WWII. The SSA left the device intact and placed it in storage.
Now in possession of the NCM, the American Dragon is believed to be the only original existing Tunny-breaking equipment, and the last surviving special purpose rapid analytic machine from WWII.
“The machine also exemplifies the joint U.S. and British code breaking effort during the war,” Mr. Allenbaugh said. “Together the two nations built a lasting relationship that is still celebrated to this day.”
The American Dragon, along with my other historically significant cryptologic artifacts, will be on the display at the National Cryptologic Museum opening later this summer. Come and decipher history when you visit our exciting new museum.