The fastest way to unlock this would be to play operation 1, mission 3 twice.
Once you start the mission, simply walk straight ahead and take the left path as soon as you have a choice to. Once on this path you will see two enemies and some mines in your path (you can kill the enemies if you want to but, you don't have to) . All you have to do is walk into the mines and you should lose all three of your troopers. There might be a chance that you only lose two of your troopers. I did this 5 times and on one of the tries, I did only lose two troopers.
I did this on easy. Fummm stated in the comments that if you do it on hard, you should lose all three troopers.
You will have to do this twice to unlock the achievement.