The Asad military base is certainly heavily guarded. Trying to drive away a plane from there, especially an AC-130 gunship, is obviously not feasible.
Planes and cars are different. Stealing a car means you can basically drive away immediately because cars definitely have gas.
But planes are different; their fuel tanks aren't always filled. Most crucially, the AC-130 is nicknamed the gunship. Why is it called a gunship? Because this type of aircraft was originally a transport plane, but was ingeniously modified by the United States into an aerial fire support plane that can unleash gunfire onto the ground in scenarios of absolute air superiority.
The specific model of gunship stationed at the Asad air base is the AC-130U. The AC-130U is armed not only with machine guns but with a 105mm cannon!
