Sledge Hammer — Walter H. Wager

“A bust-em-up gutsy book” about an elite unit of soldiers, hand-picked for a mission behind enemy lines, on a quest for vengeance (Los Angeles Times).
 
Sledgehammer is the code name for the operation of an elite OSS unit behind German lines during World War II. Five experts in guerrilla warfare are concealed under identities as a crusading journalist, a Hollywood stuntman, a professor of psychology, a money man for a major casino, and a billionaire bachelor. Their mission is clear. Their training has prepared them for anything. But when the journalist is murdered, his four friends change the plan to one single purpose: get revenge.