Another very perfect and very simple one is in the Ops Zeal challenge map. At wave 6.
At wave 6 you start at the bow of the ship with some regular soldiers walking around. Buy both Bucking Bronco upgrades. Shoot around with your machine gun to lure in some of the men. One RPG soldier shoots from the balcony at you. Use bucking bronco. Shoot the rocket at the exact moment it gets in your face. Easiest sollution, 30G in the pocket!
If you get this later in the game with more upgrades, this will be a walk in the park, finished within 10 minutes or so.