When Kenneth Levin unexpectedly gained possession of the diary his brother Ralph kept from 1965-1966 as an army doctor in Vietnam, Levin didn't know what to do with it. The tattered book wasn't much to look at, and Ralph's chicken-scratch handwriting proved virtually indecipherable. But Levin, the author of two popular Vietnam-era fictional works, kept returning to Ralph's account over and over again. There are few known Vietnam War diaries, and personal...