 He was also a psychologist with the United States Navy, (1944–46), the Department of the Army, (1946–49) and the Educational Testing Service (1967–74).One of Carroll's early projects in the 1950s involved developing a test of language aptitude (the Modern Language Aptitude Test (1953–58), or MLAT).The project grew out of the US Army's requests for a way to identify people who could easily learn foreign languages for training purposes.