Evidently written by Clive Egleton under a pseudonym. So says Wikipedia, anyway.
Grabbed this off of eBay after seeing and kind of enjoying the movie and, wow, it must be based on a slightly earlier draft of the script than the one they ended up shooting. The story is more or less the same but there are a lot of differences. On an island in Greece, the Nazis have built a P.O.W. camp around an ancient archaeological site and are using the prisoners as forced labor to excavate priceless Greek artifacts. Our principal protagonists include scientist Professor Blake and his friend Sergeant Nathaniel "Nat" Judson. They work closely with Greek resistance led by Zeno, a defrocked monk. The camp itself is run by the stern but fair Major Otto Hecht and his somewhat overzealous second in command Sergeant Ernst Mann. In the meantime, Zeno fights a clandestine war against the island's contingent of SS, led by the cruel Major Volkmann, who perform cruel and arbitrary public executions whenever they're pissed, which is all the time. And when he isn't plotting against Volkmann, Zeno is being jealous over the fact his girlfriend Eleana, the madam of the local brothel, shows an inordinate amount of attention to the thuggish Lieutenant Braun (in the movie, Braun is an SS officer serving under Volkmann, but here he's just a regular German army officer) and trying to figure out how he can take out the missile base the Nazis turned the old monastery up on Mt. Athena into. Into this blunder a pair of wayward USO performers, the Jewish comedian Charlie Dane and his kinda sorta girlfriend Dottie Del Mar.
Wackiness and a lot of violence (like, a lot more than in the movie) ensue. The one I remember the most is the fate of Nazi officer Captain Lantz. In the movie, he is overcome with the sleeping gas Zeno uses on the underground guard barracks and passes out before he can activate the alarm. He is then presumably killed when the base blows up later. In the novelization, though, he manages to make it upstairs, only for Charlie to encounter him and knock him back down the stairs, whereupon he hits his head on the stone floor and "cracks his skull like an egg." Ouch.
The cover of the version I got is slightly misleading, as the memorably creepy, almost robot-like missile launch crew with their mirrored faceplates don't appear in the book.