On the outside, it looks like a sporty version of a mid-sized Chevrolet pickup. But the Army has little interest in its camouflage-chic paint job, its custom wheels or its knobby tires. The Army wants what’s under the hood. It is not a motor. Meet the hydrogen-powered ZH-2, an experimental truck built by General Motors and recently tested by the Army at Fort Carson. It has no pistons, no cylinders. Instead it has a space-age fuel cell crammed under the hood that turns pure hydrogen into electricity to run the rig and water vapor that surges out its exhaust.