The film parallels the book with a few risqué exceptions. What is unique is that even though major actors were picked for the movie they could not be closer to the character description from the 1959 book of the same name by Howard Singer.
Russ is a schnook. Therefore if something can go wrong it will. His wife is into insurance of all kinds. She wants him to get his GI insurance while he can. After she forces him to apply (schnook), he must explain that he has two serial numbers (schnook). When he was shot down over Germany he was presumed dead and needed a second number to get discharged (schnook). So naturally realizing that the (schnook) being in the service only one-day on the second serial number, is called up to finish his time.
He ends up on an island in the middle of the Sea of Japan. There he has a revelation that saves his sanity and that of 400 other servicemen also assigned to this remote outpost. A plan, so brilliant that I am not about to tell you what it is or how it is executed.
In the book the plan cured his shnookyness; in the movie, it takes a trial. The cast includes Dick Shawn as the schnook and Ernie Kovacs as his commander and hotshot fighter pilot.
I can relate to this as I also have two serial numbers. Luckily, they were for six completed years each.