Hello Bob, welcome to myBulova. This is a remarkable watch. Quite possibly the most copied (read faked) watch out there today. Online auction sites are stuffed full of watches that want to be this one, a real, genuine, in the hands of the son of the hero who wore it, military issued watch. Congratulations to you for treasuring it and big thank you to the man who wore it. I'm not 100% sure,not being an expert on militaria, that the hands really make a difference. From it's condition I venture to guess that your father took it off when he returned home and set it aside and that it is most likely the same as it was when it was issued to him, with no later revisions.
The back screws off but I suggest letting an expert handle that task. Once we know the movement type - make sure to get a date code too - we classify it. I'm guessing it will be a 10AK like this one:
http://www.mybulova.com/watches/1943-military-issue-594
Here's an explanation of the ordance markings
Military Issue (A-10?)