Explosive Efficiency Achievement
Kill 3 on-foot soldiers with one grenade.As the description says, you need to kill three on-foot enemies with one grenade. Blowing up a vehicle with enemies inside will not count.
There will be many opportunities to earn this throughout the campaign as there are many scripted sections where there will be three enemies in close proximity. You can also coax enemies that are close to one another into gathering together by whistling or with bottles.
Note: In my experience, this did not work by changing your grenade to a sticky grenade. I had to use a regular grenade to get the achievement. Feel free to try either.
Your first opportunity occurs on Mission 1, ‘The Atlantic Wall’. As you are approaching the radio tower, there is an elaborate trench system around the front of it. On the left side while looking at the radar, there is an AA gun with three enemies looking over the trench wall. In the trench, approach the area from the east, crouching and sneaking around the right side of the AA gun. At this point, create a save in case you don’t get the achievement then throw a grenade at the middle enemy and all three should be killed. If not, reload your save and try again.
Another mission you can try this on is Mission 8, ‘Rubble and Ruin’. Using the default starting point (City Limits), run down the street and after a few seconds you will happen upon a courtyard with a statue in the middle. There will be one enemy when you turn the corner then three enemies on the far side of the statue. Silently kill the one enemy then throw a grenade into the group of enemies and they should all be killed. Once again, create a save before throwing the grenade in case all three aren’t killed.
Thanks to Trophy Tom for the video: