I read a book back in the 80's where an alien race recruited military personnel from the American, Soviet, and Israeli armed forces to fight a war against an invading species.
During flight time on a ship that can configure itself to whatever they need, the humans discovered that the "invading" species were in fact not starting an invasion, but starting their mating season. They devised a plan called Operation Yom Kippur, where they fought against the "invading" aliens, and then immediately turned around and attacked their recruiters whom ended up fleeing before the second attack began. The humans took over the ship in the end and flew home to tell their respective leaders that they no longer owe their allegiance to any one country, but to the planet as a whole.
I enjoyed this book as a kid in the 80's, but haven't seen this book on any of the science fiction and military science fiction lists, so I am hoping someone can tell me the name of the book.