After being critically wounded in Vietnam, Dr. Burstein used his variation of the Super-Soldier Serum on Tanner to save his life. The result was granite like skin and super-strength. In some regard, Burstein sees Tanner as an "older brother' to his later test subject Luke Cage. Perhaps the stress of seeing his hone village in Vietnam being destroyed and his wife being murdered or perhaps a side effect of Burstein's experiment, Mitchell Tanner soon became mentally unbalanced. 
Warhawk became an assassin used for the C.I.A. in Vietnam. He later went further insane and battled Iron Fist. After Warhawk somewhat regained his sanity he was hired to assassinate Atom-Smasher.
Warhawk was hired by the Hellfire Club to test the X-Men and bug their mansion. He snuck into the school posing as a telephone repair man and quickly took down Moira MacTaggert with a tranquilizer gun. Then he caught Professor X and Phoenix off gaurd. Warhawk took control of the Danger Room, trapping the rest of the X-Men inside. After Nightcrawler teleported out of the Danger Room with Wolverine, Warhawk battled Wolverine one on one. The rest of the X-Men escaped the Danger Room and defeated Warhawk, who was handed over to the police.
Warhawk soon became even more imbalanced and racially bigoted. He took hostages in Chinatown in New York City. He gave Iron Fist a severe beating and assassinated several citizens before being defeated and captured by Luke Cage. 
Warhawk agreed to work for SHIELD in exchange for a reduced sentence. The had him attack an AIM facility.