Lambros Demetrios Callimahos (December 16, 1910 – October 28, 1977) was a US Army cryptologist. Born in Alexandria of Greek parents, the family emigrated to the United States when he was four. His father was a journalist.
His main interests at school were in chemistry, physics and medicine.
He did not show interest in music until the age of fourteen when he entered high school in Asbury Park.
He earned a degree in law from Rutgers in accord with his fathers' wishes, but attended Juilliard at the age of nineteen and graduated with a degree in 1933. While he started at the bottom of the class, he became head of his class in his second year due to encouragement from his teacher, Arthur Lora. After graduation, he continued study in Europe.
His musical debut was in Munich in 1935 and was heralded as Meisterfloetist. He also played in Vienna and that autumn played an all-Bach programme in Munich, consisting of the seven sonatas and his own transcription for flute and harpsichord of the B-Minor suite. He had a two-year tour of recitals in Europe and was appointed to a professorship in the Mozarteum.
In April 1937, he had his first United States debut in The Town Hall. He continued to tour both in Europe and the United States.
He joined the United States Army in 1941, hoping his interest in cryptology could be put to service.
He taught Italian and cryptanalysis at Fort Monmouth. He enrolled in a Japanese course and eventually served as a Signals Intelligence officer in New Delhi.
After World War II, he was assigned to the Army Security Agency as assistant to William F. Friedman. When the National Security Agency was formed, both men joined it. During the 1950s he developed the course CA-400, an expansion of Friedman's own intensive-study course. Graduates of the course became members of the Dundee Society. As part of this course he devised the Zendian Problem. He also revised some of Friedman's own work to produce the text Military Cryptanalytics.
In 1955, he established the NSA Technical Journal and served as technical advisor for the rest of his career.
Health problems forced his retirement in 1976.