10 Decemberr 2000. See letter correcting David Kahn's comment about Frank Rowlett.

2 July 1998
Source: Hardcopy The New York Times, July 2, 1998, p. B9

Frank B. Rowlett, 90, Wizard In Making and Breaking Codes


Frank Byron Rowlett, one of the foursome who started the Signal Intelligence Service of the United States Army in 1930, died on Monday at the Wilson Health Care Center in Gaithersburg, Md. He was 90 and moved to the center last year from a retirement home in Sarasota, Fla.

Mr. Rowlett came to the rarefied world of cryptology without practical experience. But he was trained to be a mathematics teacher with knowledge of chemistry, physics, Latin and German and made important contributions to the nation's Signals Intelligence and Security system in World War II.

His proudest achievement was Sigaba, the encryption machine that was the most secure device of its kind in the American arsenal throughout the war.

He also led the team of cryptanalysts who broke Purple, the machine that encrypted Tokyo's messages to and from the Japanese Embassy in Berlin. By deciphering the code, American intelligence was able to spy on crucial aspects of Japanese diplomacy as well as German intentions and capabilities in Europe.

Frank Rowlett was born in Rose Hill, Va., and graduated in 1929 from Emory and Henry College. The next year, his academic credentials led to his recruitment by the father of modern American cryptology, William F. Friedman, as one of his original three junior cryptanalysts.

Together they made up the fledgling Signal Intelligence Service. With the American entry into World War II, Mr. Rowlett was commissioned into the Army and rose to the rank of colonel. After the war he led the intelligence division of the Army Security Agency, an S.I.S. successor.

He later joined the Central Intelligence Agency and the National Security Agency, the super-secret branch that was created in the early 1950's to make and break codes. He became a special assistant to the director of the security agency in 1958 and retired in 1965 as commandant of the National Cryptologic School.

In 1965, he was honored by President Lyndon B. Johnson, who presented him with the President's Award for Distinguished Federal Civilian Service. After Mr. Rowlett retired, Mr. Johnson awarded him the National Security Medal for breaking the Japanese code 25 years earlier. The National Security Agency's highest awards for achievement by an individual and an organization in the field of Information Systems Security were named in his honor in 1990.

Mr. Rowlett is survived by a son, Thomas M., of Frederick, Md., four grandchildren and three great-grandchildren. His first wife, to whom he was married for 50 years, Edith King Rowlett, died in 1980. His second wife, Alice Creech Rowlett, died last year.


Excerpted from Codes and Ciphers: An A to Z of Covert Communication from the Clay Tablet to the Microdot, Fred B. Wrixon, Prentice Hall, 1992

SIGABA, the U.S. Army's short name for the Converter M-134C. It was developed from a series of precedessors that were based on the electric cipher machine of Edward Hebern, who had presented his device to the Navy in 1921.

Figure 1 - 1921 Hebern
Cipher Machine

In 1925, Navy officials began a search for a machine that incorporated the Hebern wired code wheel, or rotor, but that would be better suited for inclement weather, battle, and other conditions. Experimentation led to a new cryptograph in the period 1932-34.

The improved device had five rotors each controlled by a pinwheel having 25 pins set in either an active or an inactive mode. An additional plugboard was attached to pass control from one rotor to another. Used with all five rotors and with the pinwheels set carefully, the machine was reasonably secure. It was called the Electric Cipher Machine Mark I. Its successor, the ECM Mark II, became the premier U.S. cipher machine during World War II; it was this version that was designated SIGABA by the U.S. Army.

The ECM was active during the Japanese invasion of the Philippines and the siege of Corregidor, when the defenders transmitted encrypted messages in irrelevant data such as poems, sports scores, and old news articles to confound the Japanese analysts.

The U.S. Army also used the SIGABA/ECM in a version called the M-134A (or SIGMYK). This machine had a one-time tape using a form of the Baudot code and this arrangement regulated the SIGMYK's rotors. The two-tape encryption method developed by Gilbert Vernam was also applied.

Figure 2 - SIGABA, or the U.S. Army's Converter M-134C.
(Courtesy of the National Security Agency)

To enhance Allied communications during the war, adapters were built to make the SIGABA/ECM compatable with British devices such as the TYPEX. One such adaptor, a U. S . Navy device called the CSP 1600, produced a hybrid device with five rotors designated the CSP 1700.

In the later stages of the conflict, an advanced SIGABA/ECM had 15 rotors, including 5 that gave multiple position changes to the other 10 which made the complex encryptions.


POTUS-PRIME, the name for the communication system on which Franklin Roosevelt and Winston Churchill sent trans-Atlantic cables during World War II. (POTUS = President of the United States PRIME=Prime Minister.)

Because their plans affected world history, the two leaders' messages had to be secure. Thus, early voice-scrambler methods were supplanted by a much more secure system that combined an advancement in cipher machines and Western Union technology. The equipment that made it possible was called the zero machine.

Messages from Churchill to Roosevelt were conveyed by the U. S. Army, and U.S. Navy personnel handled the communications in the opposite direction. Thus neither department had full access to all of their contents. These exchanges were assigned the letters xxxo, which indicated a higher level of priority than did the "urgent" designation.

Communiques were typed with on-line SIGABAs to produce ciphertext. They were linked by a relay box to a Western Union office. The encrypted signals from the SIGABA were brought through a transmitter distributor in this office and directly onto the trans-Atlantic cable on the first available free circuit. After the signals crossed the ocean, they were received by another SIGABA, which deciphered the material and restored the plaintext.

In March 1943, the Western Union cable became a Variplex system, allowing more than one message to be sent at the same time. However, this improvement was offset by the diminished speed of transmitting any given message when the cable was in heavy use.

A problem arose because the SIGABAs at both transoceanic locations needed exact synchronization, since false pulses along the cable produced the wrong stepping order at the decrypting terminus, resulting in nonsensical text. This was fixed by a device called a "kick eliminator," the application of which enabled the zero machine to be the swiftest, best-protected transmission of its type.

Rotors were at the core of SIGABA security. Therefore, indicators were sent with each message to tell the receiving personnel which rotor settings were necessary for decipherment. Along with the special priority designation xxxo, the sending operator applied indicator letters from a table.


From the list of three-letter groups the sender chose two, such as OKU and ECA, and combined them. In this case, the indicator would be OKUECA, the receiving SlGABA's control rotor setting would be HZAFX, and the alphabet rotor setting would be ZKQBR.


PURPLE, a U.S. codename for a Japanese cipher machine during World War II.

Figure 3 - Purple cipher machine (disassembled)

Purple was used to conceal Japanese diplomatic messages after February 1939. (It should be noted that many historians refer to the crucial 1941 Purple messages as the Purple code. Most cryptology experts refer to the mechanism itself as a cipher machine.) As tensions between Washington and Tokyo worsened, U.S. cryptanalysts increased their efforts to Herculean proportions in order to glean the secrets of this potential enemy.

The Japanese called this cryptographic mechanism 97-shiki O-bun Injiki, or alphabetic typewriter 97. (Also written '97, the date was derived from 1937, the year of its invention and the 97th year of the 25th century in the ancient Japanese calendar.) It was an advanced version of a machine known as RED and has been referred to by several historians as the "B" machine, while Red is called "A."

Plaintext was put into the 97 mechanism with an electrical typewriter keyboard. The touch of a given key sent a letter impulse on a journey through a plugboard, into an even more complex maze of telephone selector switches, and then to another plugboard that was the inverse of the input plugboard. The letter emerged as ciphertext on the output typewriter. A significant feature of this plugboard arrangement was that it was double ended--thus the output was the inverse of the input.

Late in 1938, decryptions of Red system messages announced the planned inception of a new machine cipher. A decipherment on February 18, 1939, announced that the new mechanism would be activated for Tokyo and its embassy transmissions two days later.

William Freidman and the U.S. Army's Signal Intelligence Service (Army SIS) team included Robert Ferner, Samuel Snyder, and Genevieve Grotjan. Cryptology expert David Kahn credits Genevieve Grotjan with finding important patterns or intervals that revealed Purple secrets.

For a time, this group joined Laurence Safford and the U.S. Navy s OP-20-G in a frantic attempt to decrypt the Purple messages. They were fortunate to have some comparative texts from both Red (to less important consulates) and Purple (to primary embassies).

More painstaking pencil-and-paper analysis revealed additional encryption arrangements. A very important break occurred when a technician named Leo Rosen discovered that telephone selector switches would help in tests of solution ideas.

In autumn 1940, the SIS team, including Japanese-language specialist Frank Rowlett, had developed a blueprint for what they hoped was duplication of the Japanese system (by this time the OP-20G members had been withdrawn to work on Japanese naval codes). By late fall, the first Purple analogs had been built by technician Rosen for $685.00 worth of hardware. Later versions were built with navy help.

A maze of wires and clattering relays housed inside a black wooden box, the analog was an astounding achievement of cryptanalysis and engineering, and it did indeed succeed in decrypting Japanese diplomatic exchanges.

The extent of SIS's success was realized at the end of the war, when it was discovered that the total of five Purple analogs were actually less likely to garble encryptions than were the Japanese originals. Furthermore, a captured Japanese 97/"B" machine was found to differ from the original U.S. analog by only two wire connections.


Sinkov, Abraham (1907- ), U.S. cryptanalyst and intelligence officer. A Pennsylvania native, Abraham Sinkov graduated from the City College of New York in 1927. After teaching and gaining his master's degree in mathematics from Columbia in 1929, he was employed by William Friedman of the U.S. Army's Signal Intelligence Service. As a junior cryptanalyst in 1930, he served as the SIS French specialist.

At the SIS, Sinkov worked with Solomon Kullback, Genevieve Grotjan, Frank Rowlett, and cryptographic clerk Harry L. Clark to expand the early hardwon advances of the U . S. "pencil-and-paper" analysts who were true pioneers of their craft. The new generation took on the challenges of electromechanical cipher machines and their efforts were especially fruitful against the enciphered messages of the expanding Japanese empire m the late 1930s.

By this time, Abraham had left the Washington, D.C., area to head a signals intercept station in Panama, a locale of special importance due both to its ideal position for snaring cross-continental messages and to the strategic Panama Canal.

In January 1942, with the United States directly involved in World War II, Sinkov received a crucial assignment. Now a major, he was chosen to replace the exhausted William Friedman on a secret mission to England. Accompanied by another Army Signal Corps officer and two members of the U.S. Navy's OP-20-G Cipher-solving team, Sinkov was responsible for conveying a pair of PURPLE analog machines, along with other encryption material, to embattled Great Britain. He returned with some advanced British cryptographic equipment. After a promotion to colonel, Sinkov became assistant director, then director, of the Central Bureau, a joint U.S.-Australia communications intelligence operation. With the war's conclusion, he served with SIS successor organizations, including the Armed Forces Security Agency and the National Security Agency. For a time he was the latter's deputy director of the Office of Production. After his retirement in 1962, he returned to university life as a professor of mathematics at Arizona State University.

[Figures 1 and 3 from The Ultimate Spy Book, H. Keith Melton, DK Publishing, 1996; figure 2 from Wrixon's Codes and Ciphers.]

JYA: David Kahn has tart remarks in The Codebreakers about how Friedman, and to a far lesser extent, Rowlett, got national awards for work done by others, through "well-situated friends, picayune mechanical differences, and a great but totally irrelevant record." (page 392)