AFAIK, military maps are still secret in most places. This is because they contain information that cannot be easily derived from hi-res satellite imagery. Stuff like "how much weight can this bridge support", "how deep is this ford", etc. This is important if you are trying to, say, drive tanks through unfamiliar terrain.
So I really don't get why they would make them secret.
It's helpful to know the ford depths of a river crossing before you get there with your tanks.
Take a fanciful example. One could not, say, send a U.S. Army survey team to measure the depth of the Orne before the allies landed in Normandy. The Germans would really object to that kind of thing.
