Francis Lyall "Frank" Birch, CMG OBE (5 December 1889 – 14 February 1956) was a British cryptographer and actor. He was educated at Eton College and King's College, Cambridge. During World War I, he served as a lieutenant commander with the Royal Naval Volunteer Reserve, and served in the Atlantic, the Channel and the Dardanelles before joining the Naval Intelligence Division (Room 40) from 1916-19. Birch wrote a satirical history of Room 40, Alice in ID25. Birch was appointed an OBE in 1919. In 1939, he was part of a BBC television production in a Teresa Deevy play "In Search of Valour".