During a recent trip to Seoul, I spent the morning at the Korean War Memorial Museum. The museum displays the history of conflict on the peninsula, from the Turtle Ship to the new Korean main battle tank.
The museum grounds hold various pieces of armor, artillery and aircraft, with still more inside.
Traveling note: this museum is walking distance from Yongsan Station, maybe eight-ten blocks. The admission fee is by donation. The national museum is nearby as well.