[2] 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 worked undercover in Greece until 1953, and was Chief of Station in Rome from 1959–1963 before being appointed Assistant Deputy Director for Plans under Richard Helms, holding the same post under Desmond FitzGerald.
During his time as Chief of Station in Rome, and in the course of the ongoing anti-communist operations of the CIA in Italy, Karamessines was involved in events linked to the Piano Solo, a plan for a coup d'état in the case of a communist election victory, drawn up by General Giovanni de Lorenzo [it], then head of SIFAR and the Carabinieri.
In a secret cable to Henry Hecksher, CIA station head in Santiago, dated October 16, 1970, Karamessines pointed out: "It is firm and continuing policy that Allende be overthrown by a coup ... it is imperative that these actions be implemented clandestinely and securely so that the USG (United States Government) and American hand be well hidden."
The CIA, purportedly intending only a kidnapping and not a murder, provided weapons and money to the group that carried out the operation, but General Schneider was shot during the attempt and died in a hospital three days later.