They were aping ‘The Dirty Dozen’ where Sutherland played a similar character. You have to admire a film that casts Clint Eastwood opposite Richard Burton! The most intense violence in it was the clash of acting styles.
"Oddball" is sort of a beatnik-hippie hybrid, which I guess someone figured would be required to sell a WWII movie in 1970. It's also a deliberate jab at the traditional war movie audience, which is in keeping with the overall irreverance of the film.
Kelly's Heroes is kind of like the spaghetti western of A-list war movies. Just think of that scene when they enter the bank:
Kelly throws aside the tarp, revealing a pile of wooden boxes. Then he picks up a box as all the men watch and he slams the box open. Out falls the gold. The crash of the box and then a silence. And then La Marseillaise booms from a trumpet, with close, confused shots of a matching band. Then it cuts to gritty close-ups of the principle characters: Kelly, Oddball (barking manically), the Nazi tank commander (registering excitement with a stoic German flicker of his eye), Oddball’s mechanic and Big Joe. Then the camera pans across the excited faces of the bit part actors. Across their faces gleams the reflected aura of the gold. If that wasn't intentionally a hat-tip to the style of Sergio Leone, it sure looked that way.
It's interesting that this same man directed Kelly's Heroes and Where Eagles Dare. Two great films, but as different in tone as possible.
There was nothing of enough value to soldiers in the North or South of Vietnam to risk desertion charges. The French beat us to it long before WWII started.