Who doesn't want a bit of WWII in their movie?! I think every movie would be better with war footage, say The Notebook, that would have been much better with a great battle scene. Or Driving Miss Daisy, oh yeah, that needs some massive explosions of epic proportion!
The Prelinger Archives has downloadable FREE footage for you to use how ever you see fit! Here is a little quote from their site.
"You are warmly encouraged to download, use and reproduce these films in whole or in part, in any medium or market throughout the world. You are also warmly encouraged to share, exchange, redistribute, transfer and copy these films, and especially encouraged to do so for free. "
I'm still trying to figure this out, I think everything is "free" but you have to pay for the transfer. But if you live near DC then you can go there and transfer your own films. More about this after I learn more.
If you look up stock footage this will be one of the first places that comes up. They have complied films from all the wars from WWI to Current but you have to pay for the tapes.