Tom Clancy, Without Remorse, 1993

Without Remorse is a thriller novel, written by Tom Clancy and published on August 11, 1993. Set during the Vietnam War, it serves as an origin story of John Clark, one of the recurring characters in the Ryanverse. Without Remorse introduces Clark as former Navy SEAL John Kelly and explains how he changed his name. G.P. Putnam's Sons paid $14 million for the North American rights, a record for a single book. The book debuted at number one on The New York Times Best Seller list.

In Vietnam, a U.S. target drone (specified in the book as a buffalo hunter) discovers Air Force Colonel Robin Zacharias as a prisoner of war in a secret camp administered by the NVA. Since Zacharias possesses highly classified knowledge and has been declared killed in action, Admiral Dutch Maxwell arranges a secret rescue mission for him as well as other American POWs held in the camp. Unbeknownst to them, Soviet colonel Nikolay Grishanov has been interrogating the prisoners; he later lobbies his government to transport Zacharias and his fellow prisoners into the Soviet Union, citing their intelligence value. However, friction between the Soviets and the North Vietnamese leads the latter to decide to kill the POWs. [Source]