This massive museum complex is a self-created shrine to the Tatmadaw (Myanmar military). There are three huge hangars set around a lake, one each dedicated to the army, navy and air force. Expect lots of old military equipment, some interesting displays about the independence movement and an awful lot of propaganda. It's a long way out of the city centre, many taxi drivers aren't even aware of its existence and visitors not related to the military are rare.
You will likely be shown around by a member of the military, and most people find the visit far more interesting than they expected. You will need your passport for entrance.