Frank B. Rowlett
Frank Rowlett.
Born	(1908-05-02)May 2, 1908 Rose Hill, Lee County, Virginia, U.S.
Died	June 29, 1998(1998-06-29) (aged 90)
Alma mater	Emory & Henry College
Awards	President's Award for Distinguished Federal Civilian Service (1965)
Scientific career
Fields	Cryptography

Frank Byron Rowlett (May 2, 1908 – June 29, 1998) was an American cryptologist.

Rowlett was born in Rose Hill, Lee County, Virginia^[1] and attended Emory & Henry College in Emory, Virginia. In 1929 he received a bachelor's degree in mathematics and chemistry. He was hired by William Friedman as a "junior cryptanalyst" for the Signals Intelligence Service (SIS) on April Fools' Day 1930; shortly after, he was followed into SIS by Abraham Sinkov and Solomon Kullback.

During the 1930s, after a lengthy period of training, Rowlett and his colleagues compiled codes and ciphers for use by the U.S. Army and began solving a number of foreign, notably Japanese, systems. In the mid-1930s, they solved the first Japanese machine for encipherment of diplomatic communications, known to the Americans as RED. In 1939–40, Rowlett led the SIS effort that solved a more sophisticated Japanese diplomatic machine cipher, codenamed PURPLE by the U.S. Once, when asked what his greatest contribution to that effort had been, Rowlett said, "I was the one who believed it could be done."^[2] Rowlett supervised cryptanalyst Virginia Dare Aderholdt, who decrypted the Japanese surrender message, August 14, 1945.^[3]

Rowlett also played a crucial role in protecting American communications during World War II, making fundamental and innovative contributions to the design of the SIGABA cipher machine. Its security was an important factor in saving American lives in combat. In 1964, Congress awarded Rowlett US$100,000, equivalent to $980,000 in 2023, as partial compensation for his classified cryptologic inventions.

In addition to having highly developed cryptanalytic skills, Rowlett was a good manager, and he rose quickly within the organization. In 1943–45 he was chief of the General Cryptanalytic Branch, and in 1945–1947 chief of the Intelligence Division. From 1949 to 1952, he was technical director in the Office of Operations of the Armed Forces Security Agency, predecessor to the National Security Agency (NSA).

Rowlett differed with General Ralph J. Canine, the first director of NSA, over personnel movements, including his own. Acting on his differences, he transferred to the Central Intelligence Agency (CIA) in 1952 and worked there until 1958. At that time he returned to NSA as a Special Assistant to the Director. In 1965 Rowlett became commandant of the National Cryptologic School. In 1965, Rowlett was awarded the President's Award for Distinguished Federal Civilian Service.^[4] He retired from federal service in 1966. In 1965 he was awarded the National Security Medal by President Lyndon B. Johnson for his work on breaking the Japanese Purple cipher.

Rowlett has been inducted into the Military Intelligence Hall of Fame.

Because of his importance in the protection of American communications, the Information Systems Security Organization has named its highest award the Frank Byron Rowlett Award.

Frank Rowlett died June 29, 1998, at age 90.

• Operation Gold
• Leo Rosen

 This article incorporates public domain material from Frank B. Rowlett. National Security Agency.

• Frank B. Rowlett, The Story of Magic: Memoirs of an American Cryptologic Pioneer, with Foreword and Epilogue by David Kahn, Laguna Hills, CA, Aegean Press, 1999.
• James Gannon, Stealing Secrets, Telling Lies: How Spies and Codebreakers Helped Shape the Twentieth century, Washington, D.C., Brassey's, 2001, especially chapter 6: Who Broke Purple? (pp. 94–106).