 Karamessines served in the United States Army during the World War II, but because of his knowledge of Greek language and history was assigned to the Office of Strategic Services (OSS), an organization that eventually would transform into the Central Intelligence Agency in 1948.Karamessines started out his intelligence career as analyst for the Greek Desk OSS/X2 (Counter-Intelligence) following the liberation of Greece.After the dissolution of the OSS in October 1945, Karamessines stayed on as the director of intelligence for the US Embassy, possibly at the request of Lincoln MacVeagh.