Sidney Forrester Mashbir (12 September 1891 – 13 June 1973) was a senior officer in the United States Army who was primarily involved in military intelligence. Born in New York, he served in the Arizona Army National Guard during the Mexican-American Border War. Mashbir then held several posts in intelligence positions, taking credit for catching the first German spy in the United States, before departing for on a four-year assignment as a language officer to Japan in 1920. He resigned from the army in 1923 in an attempt to execute his own master plan devised to extract intelligence from Japan in event of a war. His plan failed as a result of the Great Kantō earthquake in September 1923 and he was left bankrupt; he consequently returned to the US as an engineering businessman.