Mission 2(Operation Tonga). When you and evans get the torch and go into the bunker you will get a checkpoint right before he goes under a barrier/locker he will get ambushed. Kill the guy and quickly loot his body.
Shortly after you will enter a narrow staircase, you have to be quick! A random grenade will be thrown at you, simply run to it and pick it up and toss.
(I actually did it on veteran and instincts just told me to run to it and toss it back, I wasnt quick enough to toss back and died with it in my hand but the achieve still popped)