John Gardner's cowardly and inept secret agent, [Boysie Oakes] is sent to San Diego to witness a hush-hush submarine trial, in "Understrike" …; and the Russians send along a carefully trained duplicate to take over his place. This seems, naturally, less fresh and ice-breaking than Boysie's first case; but Gardner still brings off the trick of eating his cake and having it, presenting a neat parody and a genuine sex-and-violence thriller in the same story.

Anthony Boucher, in a review of "Understrike," in The New York Times Book Review, August 1, 1965, p. 24.