Easy way to unlock unstoppable, guaranteed
After giving up trying to get this achievement, a friend told me an easy way to unlock it. Didn't think it was possible but it worked for me last night, i'm now up 20 extra points, so here goes:
Choose the 4th map, red eye (not sure if it matters but this is the map i did it on.)
Choose your class as a grenadier, and be sure to choose C4 as one of your equipment items. Also pick the perk that grants extra C4, the other slots, weapons, etc don't matter.
When you start off, order your squad about 50 meters to the rear of the convoy (don't put them on a follow me order or board vehicle order, very important)
Next whip out the C4 and place 1 charge under each of the 4 Humvees in the convoy (if you crouch and aim just under the Humvee the charge should land under the vehicle itself)
Once all charges are in place get in your Humvee (it's important that your squad isn't in the Humvee at the same time otherwise the mission will start)
Meet up with your squad outside the blast zone. Jump out and detonate the C4 (the entire convoy needs to be destroyed)
You will fail everything and have to drive to the finish line, so get eveyone in the Humvee and floor it (you'll be shot at but just keep driving)
After Mustang says something about not getting a pizza box, the achievement will unlock, saving you potential hours of stress.