The Lockheed C-5 Galaxy is a large military transport aircraft originally designed and built by Lockheed, and now maintained and upgraded by its successor, Lockheed Martin. It provides the United States Air Force (USAF) with a heavy intercontinental-range strategic airlift capability, one that can carry outsize and oversize loads, including all air-certifiable cargo. The Galaxy has many similarities to its smaller Lockheed C-141 Starlifter predecessor, and the later Boeing C-17 Globemaster III. The C-5 is among the largest military aircraft in the world (Wikipedia).
I think that the C-5 galaxy would be a great addition to the military line of of aircraft in the game. It would also give us another large aircraft to play with, and could utilize some of the features added for the C-130, for example opening doors etc.