Lee,
The Army Ordnance Museum is at Aberdeen Proving Grounds, which is only about half an hour north of the city.
http://www.goordnance.apg.army.mil/s...anceMuseum.htm
Another cool museum is the National Cryptologic Museum (not the same as the Spy Museum in DC) at Fort Meade, about 20 minutes south of the city. Exhibits about things like hobo communication and the Navajo code talkers in WW II.
http://www.nsa.gov/about/cryptologic_heritage/museum/
Or the National Museum of Civil War Medicine in Frederick, an hour west of Balto.
http://www.civilwarmed.org/
Or the B&O Railroad museum, right in Baltimore.
http://www.borail.org/
Bill