Difficulty: Medium. Requires practice and good aim.
On the
Intel Operative Rescue mission you spend most of your time in a moving helicopter, making this difficult for anyone without a stead aim. Luckily you have infinite ammo on the helicopter.
Use your pistol on this, as it's a non-lethal kind (Press down on D pad to select it). You must disable EVERY enemy with this, though it isn't required to actually shoot EVERY enemy in the mission, just the ones who are an issue. With cars shoot either the driver or the wheels to disable.
Don't worry about the car that drives into an explosive barrel, this always happens and the driver clearly survives as the trophy still unlocks.
When you get down from the helicopter move all enemies away from the fuel tanks where the tank will greet you BEFORE getting the rocket launcher. This is the only thing on the level you can use that rocket launcher on (And it takes 3 shots so don't waste any as you only have 4).
Here's a vid to help.
https://www.youtube.com/watch?t=540&v=kJWTyXr1XS8