On one of his trips back to the U.S. in December 1967, Vann was asked by Walt Rostow, an advocate of more troops and Johnson administration National Security Advisor, whether the U.S. would be over the worst of the war in six months: "Oh hell no, Mr. Rostow", replied Vann, "I'm a born optimist. I think we can hold out longer than that." Vann's wit and iconoclasm did not endear him to many military and civilian careerists but he was a hero to many young civilian and military officers who understood the limits of conventional warfare in the irregular environment of Vietnam.