on Charlie Don't Surf you can take a right path where there is a car by a wall*...there is almost always two enemys hiding behind the car just grenade it and voila... achievement unlocked
*I think it is near the beginning of the level, after a large bit of barbed wire has been pulled along a road**
**This is about 2 years after I played, unlocked and wrote this solution. My memory isn't perfect so any clear up of this would be helpful.