Aberdeen Proving Grounds has a museum that while small is top notch. Aberdeen is the home of the US Army testing and proving grounds so most captured weapons eventually found there way there and a lot of them are in the museum. As far as I know, it is free. They have several rail guns, V1 and V2 rockets, a lot of tanks and artillery pieces and an indoor museum that has small arms, etc. If they allow it (security issues) there is a tank row which contains nearly every US tank made and or tested so there are a lot of prototypes on display. This is not exactly part of the museum but is located in the median strip of a road going into the post. Located in Maryland just north of Baltimore.