The Germans referred to the U.S. machine, SIGABA, as the 'Big' machine, hence the name of this exhibit. The collection of 'Big' machines in the exhibit encompasses several different, high-level, encryption machines used during World War II by the U.S. and its adversaries. 'Big' machines of this era were generally suited for fixed-station or ship-borne secure communications.
SIGABA/ECM
The
U.S. Army's SIGABA, called the ECM (Electric Cipher Machine)
in the Navy, was the only machine system used during World War II
to remain completely unbroken by an enemy. It utilized the same principle
of rotating, removable, wired rotor wheels that the German Enigma employed.
However, unlike the stepping motion of the Enigma, the SIGABA/ECM's
motion appeared to be random. It wasn't, but it was so
complicated, the German's never broke it, and the Japanese
gave up trying.
Frank Rowlett of the Army's Signal Intelligence Service developed the complicated stepping motion. Ten of SIGABA's twenty rotors could be taken out and moved to a different position; the rotors could be placed in the machine either "forward" or "backward;" and any one or more of the rotors could move with each keystroke. This differs dramatically from the predictable motion of the Enigma that required its first rotor to move one step with each keystroke and the other rotors stepped in sequence. This proved to be one of the greatest flaws in the Enigma, a lesson the Americans learned and were able to improve on when developing their SIGABA/ECM.
Tunny and SturgeonThe Tunny and Sturgeon machines (referred to by American and British cryptologists as the "Fish" machines) were both on-line cipher machines. Messages could be simultaneously enciphered and transmitted, saving a great deal of time. Although a British cryptanalytic attack made considerable progress, the results were far slimmer than against the Enigma, both because the difficulty of attack yielded fewer breaks and because a lot less traffic was sent over these systems.
The Tunny (which is British slang for Tuna) was a German Army machine that could be used out of the back of a truck as well as at a fixed site. To create its encryption, the Tunny used the international telegraphic "Baudot" cipher and an additive placed on the cipher by the rotors. It was used to stream high-level teleprinter messages. The British built the first large valve programmable computer, Colossus, to decrypt Tunny messages, cutting decrypt time from weeks to hours.
The Sturgeon was primarily a German Air Force system. It was capable of high-speed teleprinter transmissions. This particular machine used cable rather than radio to transmit its messages, thus decreasing the Allies' ability to intercept. A Swedish mathematician, Arne Beurling, was the first to break the Sturgeon, a feat he accomplished in just two weeks.
Intended for high-level encryption, the Japanese family of machines using telephone selector switches came to be known in the United States by their 'color' codenames: Coral, Jade and Purple. The switches performed the same function as a wired rotor, stepping forward through each of the 25 contacts. However, unlike wired rotors, the switches could not be taken out and rearranged, a serious limitation to the system. The Japanese Imperial Navy used the Jade machines for its high-level encryption of the katakana syllabary. Its keyboard used a shift key and 25 letter keys to create the 48 characters. Most machines were aboard ship, but this Jade was captured on Saipan when U.S. forces took the island in June 1944.
The Japanese diplomatic system, codenamed Purple, differed from Jade in that it included a plugboard. Twenty letters could be plugged and routed through three units, while the other six letters went through only one. For the Army's Signal Intelligence Service, breaking of the "sixes" was not terribly complicated; however, the "twenties" appeared to be completely different from any known system. After determining that telephone-switching units could be the basis for the machine, the cryptanalysts, after 18 months of analysis, eventually broke Purple. Some believe this to be the greatest feat in cryptologic history.
On display is the Army's first analog machine used to decrypt Purple enciphered messages. This machine solved the famous fourteen-part message telling the Japanese ambassador to break relations with the United States on December 7th at 1:00 p.m. Although it arrived on the night prior to the attack on Pearl Harbor, the Japanese did not decipher it until after noon on December 7th and were unable to present it to the U.S. until after 2:00. The Signal Intelligence Service, using this analog, had decrypted the message by 5:00 a.m. Unfortunately, it contained no military information concerning an attack, just an end to diplomatic relations. War was clearly imminent, but the message lacked details.