HomeAbout UsCryptologic HeritageNational Cryptologic MuseumExhibit Information

National Cryptologic Museum

Exhibits & Artifacts

For images of many of the exhibits listed below, please visit our National Cryptologic Museum Current Exhibits Image Gallery.


18th Century Cipher Device

The National Cryptologic Museum acquired this cipher device from a West Virginian antique dealer, who found it in a home near Monticello. Thomas Jefferson described a similar device for the English language in his writings, and it is sometimes referred to as the "Jefferson Cipher Wheel." However, the connection to Thomas Jefferson remains unproven. Jefferson's design was probably based upon an unnamed earlier device. The device uses scrambled alphabets on the edges of each wheel to cipher a message. By aligning the plain text letters in one row, any other row can be selected as the cipher text. The wheels are individually numbered and can be placed on the spindle in any prearranged order. This particular artifact is thought to be the oldest extant true cipher device in the world. It was apparently for use with the French language, the world's diplomatic language used through World War I.

African-American Experience

This exhibit of the experience of African-Americans at NSA and its predecessor organization mirrors the African-American experience in the United States and the federal government in the latter half of the twentieth century. The first African-American hired by the Army Security Agency, and who later made the transition to the Armed Forces Security Agency, worked first in a segregated office. Senior supervisors were white. They performed menial tasks not wanted by whites. In the 1950s, African-Americans began to move into the mainstream workforce. The segregated office was abolished and more African-Americans received supervisory positions.

American Civil WarPlay Civil War Signals Video hosted on NSA YouTube Channel (8:15)

This exhibit celebrates the important role that cryptology played during the American Civil War. During America's first century, secret writing — cryptography — figured in many instances in which lives and fortunes were at stake and confidentiality was desired. Until nearly the middle of the 19th century, large armies moved over an extensive battlefield unassisted by any special technology to aid long distance communications or even tactical communications. In 1844, Samuel F. B. Morse successfully tested his improved electromagnetic telegraph between Washington and Baltimore. At the time of the American Civil War, both sides began encrypting high-level messages to be transmitted on the telegraph. Both sides established cipher bureaus in their respective capitals to work on enemy encrypted messages, one of the early examples of a centralized intelligence activity in the United States.

American Civil War: U.S. Army Signal Flag

This star flag, displayed in the Museum, is a rare item. This flag is only one of two known to exist today in which all five points have been adorned with battle names. This special flag was awarded only to Signal Corps officers who distinguished themselves in combat. In the late 1850s, Albert J. Myer, an Army doctor, invented a method of communication using line-of-sight signal flags. Employed widely during the Civil War, the Myer flag system became the origin of the Army Signal Corps. Using various positions of the flag to represent letters of the alphabet, soldiers would wave them to send messages to other units. Union and Confederate soldiers became proficient in the Myers' system, known as wigwag. Soldiers had to be in an elevated location to be seen. Since the system is visual, messages could be intercepted and this forced encryption.

American Civil War: Union Code Book

Although entitled Cipher for Telegraphic Correspondence, this book is actually a code book. It was used by Union General Joseph Hooker's code clerk and is one of the few books whose provenance is known. Important names, places, and military terms have two different code names. A code changes a word or phrase into a different word, phrase, or number group; a cipher substitutes each individual letter for a different letter, number, or symbol.

American Revolutionary War: Revolutionary Secrets

This exhibit showcases how the Revolutionary Army leveraged cryptology during the war. America's independence was achieved with the help of codes, ciphers, invisible ink, visual communications, and hidden messages. These techniques, practiced by the colonists and the British, protected communications vital to the commanders. They disguised information needed to plan strategy, report the enemy's capabilities, and provide warnings. Solving and reading the enemy's secret messages also proved critical. Not only did it reveal the enemy's intentions, but a few even revealed American traitors.

USAF C-130

This exhibit recounts the history of the Soviets' shooting down an American reconnaissance aircraft on September 2, 1958. Soviet MiG-17 pilots shot down the USAF C-130 when American pilots strayed into restricted airspace over Soviet Armenia. It was supposed to fly a "race track" pattern between the Turkish cities of Trabzon and Van essentially parallel to the Armenian border. Initially, the Soviets denied shooting down the aircraft, claiming the plane and its 17 crew members "fell" into their territory. It was not until the end of the Cold War that they released previously classified documents indicating that all 17 U.S. personnel had died in the crash. An Air Force C-130 was refurbished and painted to match the markings of the down aircraft, #60528. It was flown to Fort Meade and dedicated at the National Vigilance Park on September 2, 1997.

U.S. Army RU-8D

The National Cryptologic Museum displays a mock-up of the interior of a small, reconfigured Army aircraft, the RU-8D. The plane was one of many different types of aircraft used by the Army to conduct its reconnaissance missions. Most of the missions were in support of tactical operations conducting short- and medium-range direction finding and signals intelligence. The RU-8D significantly advanced the electronic collection mission with its onboard navigation system and improved antennas.

Cold War: GRAB II Elint Satellite

The GRAB II (Galactic Radiation And Background) satellite depicts one of the earliest signals intelligence satellites launched by the U.S. Government. The first GRAB satellite was launched on June 22, 1960, following the loss in May of the U-2 spy plane flown by Gary Powers. The successful launch of the GRAB II satellite occurred on June 29, 1961. The GRAB satellites had a dual mission. The unclassified mission was to gather solar radiation data. The secret mission gathered radar pulses within a specific bandwidth from Soviet equipment. The data was then downloaded to ground stations, recorded on magnetic tape, and couriered to the NRL, whose engineers had designed and built GRAB. Following initial analysis, the tapes were duplicated and sent to Strategic Air Command and the National Security Agency (NSA). Based on the information NSA received, analysts determined that the Soviets had radars that supported the capability to destroy ballistic missiles.

Cold War: Great Seal

On August 4, 1945, Soviet school children gave a carving of the Great Seal of the United States to U.S. Ambassador Averell Harriman. It hung in the ambassador's Moscow residential office until 1952 when the State Department discovered that it was 'bugged.' The microphone hidden inside was passive and only activated when the Soviets wanted it to be. They shot radio waves from a van parked outside into the ambassador's office and could then detect the changes of the microphone's diaphragm inside the resonant cavity. When Soviets turned off the radio waves it was virtually impossible to detect the hidden 'bug.' The Soviets were able to eavesdrop on the U.S. ambassador's conversations for six years. The replica on display in the Museum was molded from the original after it came to NSA for testing. The exhibit can be opened to reveal a copy of the microphone and the resonant cavity inside.

Cold War: U-2 Incident 

The National Cryptologic Museum has the only piece of Gary Francis Powers' aircraft on display in the United States. It was given to the Museum by the Armed Forces Museum in Moscow where the plane's wreckage is exhibited. On May 1, 1960, while flying a CIA reconnaissance mission in a U-2 reconnaissance aircraft, Powers was shot down over the Soviet Union. Although he parachuted to safety, Powers and his plane wreckage were captured. Soviet Premier Nikita Khrushchev accused the United States of spying. The international turmoil resulted in the cancellation of a summit meeting scheduled between President Eisenhower and the premier.

Cold War: U.S.S. Liberty

The Museum displays the flag that flew at the time of the attack of the U.S.S. Liberty, a U.S. Naval Ship, on June 8, 1967, when the ship found itself in the middle of the 1967 Arab-Israeli Six-Day War. Cruising 25 miles off the Gaza coast, it was attacked by Israeli fighters and torpedo boats at 2 o'clock on a clear and sunny day. There was no apparent provocation, and the reason for the attack has never been fully resolved, although Israel described it as an identification error and sent restitution for the damage and loss of life. The U.S. government accepted the explanation of the Israeli government concerning the identification error. The loss of 34 men was the largest loss of life in a single event in American cryptologic history. It occurred, ironically, during a war in which the United States was not a participant.

Cold War: U.S.S. Pueblo

The Museum displays the history of the attack of the U.S.S. Pueblo. Following the war between the two Koreas in the 1950s, the United States continued to support South Korea. In an effort to gather intelligence about North Korea's intentions, the U.S. Navy began operational cruises with AGER ships outfitted with reconnaissance equipment. On January 23, 1968, while in international waters off the Korean coast, the North Koreans attacked the Pueblo. One man was killed while destroying cryptologic materials and three men were wounded. The 82 crewmen were held for 11 months before being released. The ship remains in North Korea to this day and it represented the largest single loss of such sensitive material. It compromised a wide range of cryptologic and classified documents and equipment.

Cold War: VENONA

The National Security Agency released declassified copies of VENONA messages. All of the released documents are available for review at the Museum Library and some significant messages are part of museum displays. In February 1943, the U.S. Army's Signal Intelligence Service, a forerunner of the National Security Agency, began a small, very secret program, which was eventually code named VENONA. The object of the VENONA program was to examine, and possibly exploit, encrypted Soviet diplomatic communications. Analysis of the messages revealed that some of the messages were from KGB and GRU operatives working undercover in the United States.

VENONA and the Rosenbergs

The Museum display includes photographs of American citizens who gave information to the Soviet KGB, replicas of the messages revealing the espionage, and some World War II-era artifacts similar to those used by KGB officers. The Rosenbergs case was controversial, partly due to the accusation and conviction of Ethel Rosenberg. VENONA messages indicate that her husband, Julius, was heavily involved in providing information to his KGB handler. At least one message shows that Ethel may have known about her husband's activities. Ethel's brother, David Greenglass, was also involved, selling details about the atomic bomb project in Los Alamos where he worked. It was David's testimony against his sister and brother-in-law that led to the conviction of the Rosenbergs for conspiracy to commit espionage.

Computer Development: Cray Supercomputers

On exhibit in the Museum are two Cray supercomputers. NSA has been a leader in computer development throughout its history. Some of the earliest supercomputers were designed and built specifically for the National Security Agency. The XMP-24 on display is the upgrade to the original XMP-22 that was the first supercomputer Cray ever delivered to a customer site. It was in operation from 1983 to 1993 and was arguably the most powerful computer in the world when it was delivered. The second generation Cray, the YMP, replaced the older version in 1993. In 1993 most personal computers held only 16 million bytes. The YMP used vector processing, a very powerful form of overlapping, parallel processing to conduct 2.67 billion operations per second. The YMP was decommissioned and went on display at the Museum in 2000.

Computer Development: Harvest Tape Drive

This Museum displays one of NSA's earliest work with super computers. In the 1950s NSA collaborated with IBM for computer development. The result of this collaboration, HARVEST, went on line in 1962 and was finally retired in 1976. IBM built a new, state-of-the-art second-generation general-purpose processor. To be successful, HARVEST had to have a super high-speed memory and high-speed tape drives, beyond anything then in existence. Developed over a five-year period, the most innovative component was TRACTOR, the high-speed tape drive system. It was the first fully automated storage and retrieval system and a precursor to some of today's storage systems, such as StorageTek.

Computer Development: RISSMAN

RISSMAN was a telemetry processing system, built in the early 1980s featuring custom-designed hardware. As part of NSA's SIGINT mission, telemetry signals were collected by various platforms. Magnetic tape recordings of the intercepted signals were then sent to NSA's National Telemetry Processing Center for processing. These measurements were then sent on computer tape to various analysis centers which identified the function of the various transducers and developed performance estimates. This data was used to formulate defense policy and guide treaty negotiations.

Computer Development: StorageTek

The Storage Technology Corporation produces some of NSA's recording media storage libraries. This machine is an example of an automated tape cartridge system. It was designed for large, complex, high-performance environments, such as NSA's. It has the capacity for 6,000 tape cartridges each holding 50 gigabytes of data: a total of 300 terabytes (300 terabytes would fill enough 8.5×11 paper to circle the globe more than 3,000 times!). Using a robotic arm, this StorageTek machine is capable of exchanging 175 cartridges per hour.

NSA/CSS Cryptologic Memorial

The National Security Agency/Central Security Service Cryptologic Memorial exhibit is a replica of the black granite wall found in the NSA Headquarters building at Ft. Meade, MD. It is intended to honor and remember those who have given their lives, "serving in silence," in the line of duty since 1950. The Memorial was built in 1995 and lists the names of those cryptologists, military and civilian, who have made the ultimate sacrifice. The Memorial Wall was designed by an NSA employee and is 12 feet wide and eight feet high, centered with a triangle. The words "They Served in Silence," etched into the polished stone at the cap of the triangle, recognize that cryptologic service has always been a silent service — secretive by its very nature. Below these words, the NSA seal and the names of 177 military and civilian cryptologists (as of 01/19) who have given their lives in service to their country are engraved in the granite. The names are at the base of the triangle because these cryptologists and their ideals — dedication to mission, dedication to workmate, and dedication to country — form the foundation for cryptologic service.


The Museum displays an example of modern encryption efforts in the Protecting America's Secrets gallery. The National Security Agency-developed Secure Mobile Environment Personal Encryption Device (SME-PED - pronounced SMEE-Ped) is a secure smart phone that provides secure, portable access to classified information systems enabling users to send and receive both classified and unclassified telephone calls and email. It also gives users access to browse the Internet or secure web networks that are classified SECRET. It all fits in the palm of your hand. Working under a National Security Agency contract, General Dynamics developed the SME-PED for use by top-level leaders in the Department of Defense, Homeland Security, State Department, and even state governors.

Friedman, Safford, and Washington

This exhibit celebrates three heroes of cryptology. William F. Friedman worked for the U.S. Army to make codes and took on the additional task of codebreaking. He assembled a brilliant team of cryptanalysts that broke the Japanese diplomatic cipher machines that had replaced their earlier paper codes. Friedman is regarded as the father of modern American cryptology, having pioneered in communications security and cryptanalysis, and being a great teacher of the art. What William Friedman was to the Army, Laurance Safford was to the Navy. Beginning in the mid-1920s with a staff of one (civilian cryptanalyst Agnes Driscoll), Safford assembled the nucleus of the team that broke the Japanese naval codes during World War II. George Washington, while never a codebreaker himself, recognized the value of military intelligence and used the secret arts, including codebreaking, in the epic struggle against Great Britain during the Revolutionary War.

Hall of Honor

The Hall of Honor was created in 1999 to pay special tribute to the pioneers and heroes who rendered distinguished service to American cryptology. The standards are high for induction into this great hall. The individuals honored were innovators over their entire careers or made major contributions to the structure and processes of American cryptology. The men and women who have been inducted to the Hall of Honor are all greats in the once silent world of cryptology.

Hobo Life

The origins of the term "Hobo" cannot be traced, but came into common usage by the end of the 19th century. Following the American Civil War, many veterans took jobs building the expanding railroads. Men climbed aboard the freight trains in search of work. In some places, hobos who drifted into town were not always welcome. In other places, they found those who were friendly and willing to help. Knowing where to go or whom to avoid was important to these travelers. So the hobo community developed a written communication system of signs. A symbol on a fence post, mailbox, or tree told other hobos what to expect in the town or from the homeowner. See samples of hobo signs.

Hobo Communications: A Brief History of Hobos and Their Signs

The origins of the term "Hobo" cannot be traced. A few suggestions have been put forward. Some say it comes from "Hoe Boy" because many migrant workers traveled with a hoe or other farming tool. Others claim it came from the soldiers returning from the Civil War, who were "Homeward Bound." Some suggest it is from the congenial greeting "Hello boy" that changed to "Lo boy" and "Lo bo" and finally to "Ho bo." Others think it came from the word hoosier, meaning a rustic individual, a frontiersman. There are even those who say it comes from the Latin Homo Bonus, meaning good man, or the French haut beaux, the highest of the handsome. Few, if any, of these explanations seem adequate.

However the term "Hobo" originated, it came into common usage by the end of the 19th century. But the history of hobos began decades earlier. Though not called hobos, but frequently referred to merely as tramps, men had long been traveling around picking up work. Most modern hobos, however, trace their lineage to the building of the railroads and the end of the Civil War.

Many Civil War veterans couldn't, or didn't want to, return home and took jobs with the expanding railroads. Between 1866 and 1873, 35,000 miles of new track was laid across the country, much of it as part of the Transcontinental Railroad. The laborers moved west with the track that they laid.

The Panic of 1873 and the depression that followed led men to climb aboard the freight trains in search of work. Jumping on slow-moving freights, they moved across the country following the different harvest seasons or working in mining or lumber camps. The situation repeated itself with the Great Depression of the 1930s. Thousands of men in search of work took to the rails and roads.

One trait hobos have in common is that they travel and work. They take pride in this attribute and often travel with the implements of their trade. In the 1880s, they began to distinguish themselves from "tramps" and "bums." Hobos have a work ethic. They willingly work for pay or food. In fact, they travel around the country as workers, not only because they enjoy the freedom, but also to earn a stake to get them through the winter. Tramps, as defined by the hobos, are people who travel, but prefer not to work, and bums neither travel nor work.

Although inextricably linked with the trains, some hobos traveled by car, others on foot. They traveled to work and worked to travel — the lifestyle of a hobo. A hobo's life could be exciting and dangerous, fulfilling and lonely, easygoing and difficult. The hobos sought not only employment, but also the freedom and independence the life allotted them. But that life also came with hardships and danger.

Not only is hopping a train illegal, it is extremely dangerous. Many hobos were killed or injured while trying to board or jump off a moving freight train. Others became locked inside box or refrigerator cars, their bodies found weeks later. Some hobos found places on trains to hide from the "bulls" who policed the cars, only to be crushed when the freight shifted. Still, despite the inherent hazards, thousands of hobos in the Depression made "rail riding" their chosen form of transportation.

Among the hardships of the hobo life were the attitudes and prejudices hobos faced from the townspeople and farmers they met along their way. All hobos felt the anger of local residents who thought hobos were lazy tramps looking for a free handout or were taking work from local men. Black hobos faced additional discrimination. However, during the Depression, the prejudice and ill-treatment they endured came more often from the law rather than from their brethren hobos. Although very few in number, women hobos faced the fear, and occasional reality, of assault in addition to the dangers and hardships the male hobos suffered.

In some places, hobos who drifted into town were not always welcome. In other places, they found those who were friendly and willing to help. Knowing where to go or whom to avoid was important to these travelers. However, hobos' paths crossed infrequently, so the hobo community developed a written communication system of signs. Mysterious and temporary, these signs helped hobos move more safely around the country looking for work. A symbol on a mailbox, fence post, signpost, or tree told other hobos what to expect in the town or from the homeowner.

The origin of the signs, like the Hobo name, is lost to history, but some of the symbols and their meanings have been documented. Carl Liungman's Dictionary of Symbols makes a connection between the hobo signs in the U.S. with those in England and the gypsy signs used in Sweden. A few of the symbols are the same. Several look the same, but have a different meaning. And still more are completely different, even if the information being relayed is similar. Like any language, written or spoken, over time it develops independently to meet the needs of those using it.

What's interesting to note, as Liungman points out, is that the system developed at all. Hobos, in general, travel alone and enjoy their independence. And yet, they still congregate in hobo jungles or travel with an occasional partner only to split when they decide to go a different way. Despite this preference for solitude, they still feel a certain camaraderie with their fellow hobos, an obligation to assist their brethren — thus, the creation of the signs and symbols.

Some of the signs appear to have a visual connection to their meaning. A drawing of a top hat means a wealthy man lives here. Others seem to indicate no relationship between the meaning and the symbol. A good code system makes no intuitive correlation between the code and its meaning. However, this then requires an explanation for the intended user. The definitions and explanations of the approximately 50 different hobo signs had to be passed on. Perhaps experienced hobos told young men what to look for as they traveled in a boxcar or sat at the campfire of a hobo jungle near a train yard.

The signs relayed information concerning a variety of topics important to the hobo. Symbols indicated where one could find a meal and whether work would be required first. Some signs described whether the police in town were friendly or that a hobo should keep moving. During the depression of the 1930s, Prohibition was also the law. Signs told whether a town was "dry." Other symbols marked a good location to catch a train. All of it was information a hobo could use.

The signs were intentionally temporary. Hobos used chalk or charcoal to mark an immediate location. The signs wore off in time. This may have been because situations were frequently in flux. A farmer may initially be helpful, but later, as resources or work diminished, he may order the hobo away. A woman who first took pity from a hobo's sad tale may become hardened after hearing too many.

No one knows exactly when or how the signs were created, nor are they in use today. Information for today's hobo is equally important, but in our modern world even the hobos make use of the communication systems on the Internet. With free access available in many libraries and community centers, hobos are no longer dependent on chalk marks. They have websites and email to share details of their travels and upcoming hobo events.

Interestingly, however, chalk marks similar to the hobo signs sprang up in 2002 precisely because of the Internet. "Warchalking" used symbols to mark areas of unsecured wireless networks. Like the hobos of the 20th century marking a good place to hop a freight train, just a few years ago travelers with a wireless card could, in some cases illegally, make use of these unsecured nodes for their PDAs and notebooks. The practice of "warchalking" was short-lived, however. New technological advances in wireless security and the advent of accessible Wi-Fi Zones put an end to the need for "warchalking." Wi-Fi Zones are widely available to travelers and, in some cases, are free. Their locations are clearly and more permanently marked than any hobo sign ever was.

Despite the many predictions that hobos would soon be a thing of the past due to the reduction in railroad lines, the faster diesel trains, and few jobs for seasonal workers, hobos still exist today. Some still engage in the dangerous and illegal practice of hopping freight cars; others drive the roads. Today, signs of hobos can be found in places like bridges and overpasses written in permanent marker. They may list the hobo's name, date, and his next destination. But gone are the secret signs and symbols of their predecessors.

The Kahn Collection

Dr. David Kahn, cryptologic historian and author, graciously donated his vast collection to the Museum, through the National Cryptologic Museum Foundation (NCMF). Included in our exhibit are two of the original drafts of his seminal work, The Codebreakers, which Dr. Kahn wrote, and rewrote, before its publication. Dr. Kahn collected books, artifacts, articles, and material as his research progressed over the years. A few of the more interesting or unique items are now on display: autographed copies of Elements of Cryptanalysis by William Friedman and The American Black Chamber by Herbert Yardley; a French manual on protecting private conversations; and, as an example of the eclectic and diverse nature of collection, a Nazi propaganda program.

Korean War

The Museum displays a brief history of the role cryptology played in Korean War. In 1945, Korea was liberated from Japan, but split in two. The Soviet Union aligned with North Korea, the Democratic People's Republic of Korea (DPRK). The United States allied with South Korea, the Republic of Korea. On June 25, 1950, the North Koreans invaded the south. The conflict continued for three years ending in 1953 with the signing of an armistice agreement. Communications Intelligence played a role throughout the Korean War. The predecessor to the National Security Agency, the Armed Forces Security Agency (AFSA,) analyzed Chinese civil communications, employed sound-detecting devices, and deployed intercept sites near North Korea.


This exhibit stresses the importance of language in the National Security Agency's mission. The exhibit has two major themes. First, the exhibit explores the complexity of languages and provides facts on characteristics and relationships of diverse languages of the world. The exhibit features a replica of the Rosetta Stone, the key to understanding Egyptian hieroglyphics, which was incomprehensible for nearly 2000 years before its discovery. Second, the exhibit offers a glimpse of the intricate world of cryptologic language analysts and their critical role in helping policymakers and warfighters defend our nation. It explains the complex and interesting process used by cryptologic language analysts in solving cryptologic problems.

The Magic of Purple

Purple Fact Sheet

This Museum exhibit highlights one of American cryptology's greatest achievements. In the mid-1930s, Frank Rowlett, the senior member of the group, headed up a robust effort to break the first of two important Japanese diplomatic systems, which was called Red. After successfully breaking the Red cipher, the team discovered that Japanese diplomatic messages were being transmitted on a new system called Purple. To conquer Purple, the team needed to build a device that could mimic the machine's scrambling pattern. The breaking of Purple would be of immense help in understanding Japan's diplomatic strategy before Pearl Harbor.

History of Purple

On a June morning in 1930, William Friedman, Chief of the Army's Signals Intelligence Service (SIS), and three members of his staff headed down a long corridor in a deserted part of the Munitions Building. Throwing open the two large doors that led into the vault area, Friedman lit a match and announced, "Welcome, gentlemen, to the archives of the American Black Chamber."

Established in 1919 the Chamber had once been America's main cryptologic workhorse. Friedman hoped to determine if any of the information found in the Chamber's files could shed light on current Japanese systems.

By the mid-1930s, Frank Rowlett, the senior member of the group, headed up a robust effort to break the first of two important Japanese diplomatic systems. Dubbed the Red Code, the elements of the system were a mystery. For months, Rowlett and his team endured long days and even more sleepless nights. Finally, a breakthrough occurred one evening. Rowlett remembered that from the hundreds of messages he had examined, three in particular were exceedingly long. If by chance those messages were enciphered on the same particular machine, it might be possible to discern a pattern that resembled certain Japanese words.

The following morning, the team put Rowlett's epiphany to the test. By noon they were on their way to solving the Red Code. But the benefits culled from the Red Code would only last so long. In 1939 the Japanese upgraded to a new machine driven cipher that SIS called "Purple." Despite their earlier success, the team realized that Purple was more complex than the previous Red system. For the next 18 months the codebreakers were in the dark.

Thankfully, for a brief period the Japanese used both the Red and Purple machines on some diplomatic circuits. By monitoring specific stations, the team could predict the first few words of each message. Using the many "cribs," as the cryptologic clues were called, the team discerned that, in the text of Purple messages, six letters were always treated differently than the other 20. Through pen and paper analysis, the team regularly uncovered the shuffling sequence and determined which of the six letters stood apart from the other 20 each day.

But pen and paper analysis was not fast enough to crack the system on a timely basis. To conquer Purple, the team needed to build a device that could mimic the machine's scrambling pattern. The fact was, however, that no westerner had ever seen a Purple machine.

The challenge of building the device fell to Leo Rosen, an MIT educated Army officer. One day, while leafing through an electrical supply catalog, Rosen noticed a device called "the uniselector." The device consisted of six telephone stepping switches bunched together that ran through 25 contacts. Quickly, he ordered two of the devices built, what would come to be known as, the "six buster."