If you are looking for something to help with a school paper then a single documentary is not the way to go. Books would be more helpful and easier to find, however if you insist on being lazy you will want to watch at least 5 different documentaries.
If you are doing this for personal interest then band of brothers and the pacific, while not completely factual, are based on the lives of real soldiers and are a really good look at the stuff that went down.