Day of the Guns, first of Mickey Spillane’s four Tiger Mann espionage thrillers written 1964-1966.
Not surprisingly the formula is not all that different from Spillane’s Mike Hammer novels. There’s plenty of sex and violence. Tiger Mann resembles Mike Hammer in that he gets personally involved in a case and the case quickly becomes a kind of one-man crusade.
Great fun.
My review: https://vintagepopfictions.blogspot.com/2017/01/mickey-spillanes-day-of-guns.html