Prototype

Another trophy that you should easily get before you complete the story mode. But if not, it should come as you complete other trophies involving military vehicles (Misconception, Threat Elevated, Surface-To-Air, etc). Or you can either look for helicopters in the sky and hijack them with your Longshot Grab, or go to either military or infected areas and steal some tanks. No matter how you choose to do it, this is fairly simple.

You can track your progress under the Statistics -> Hijacks page on the pause menu.