This achievement is done in the mission called Sabotage in the Loue Valley.
You start the mission just outside a small settlement, then must move through a lumberyard, blow up a bridge, then you will come to a castle. The achievement takes place inside. There are no missable vehicles that will drive away, they are not especially hidden from you, nor will you be impeded in any way besides getting shot at by Nazis.
There are six trucks, two half tracks, and a tank that you must blow up. Only the half tracks and tank will appear on your minimap so you must find the six trucks on your own. The achievement pops the moment you blow up the last vehicle, so if you thought you were done and received no achievement, then you missed one.
Step by step if you need the assistance:
*** Spoiler - click to reveal ***As soon as you enter the castle there is a parked truck to the east, and another truck driving down the road past it to park directly north of you. After blowing these up, head up the road that the truck was driving on, and immediately after the road bends north, there are two more trucks to the west.
Behind the truck to the north is a cache of grenades and timed explosives. You will need these, so collect them before blowing up these trucks. After grenading them, get back on the road and follow it north to the first vehicle marker on your minimap, which is the first half track. Do not use grenades on it, since you will need several and will waste your stock. Plop a timed explosive on the halftrack and continue along the road to the northwest, through a large archway.
You will see a tank on your left and a truck on your right. As with the halftrack, grenades are wasted on it so plop a timed explosive on it instead. Grenade the truck and continue following the road as it turns southwest.
The final vehicle marker on your minimap is the second and final halftrack, and parked right next to it is the final truck and the final vehicle for the achievement. You're going to get a two-fer regardless of how this plays out, so you can choose to either grenade the truck to collateral the halftrack or put a timed explosive on the halftrack to collateral the truck. Either way, once they explode, your achievement should unlock.