This achievement is tied to the "Armored and Dangerous" side mission. In this mission you need to take down 9 militia APC cars. They are scattered around the 3 islands of Gotham. There are usually 3 on each island.
check your mission wheel from time to time between the main missions by pressing
. You will quite often find the word "intel" written below the icon of the mission. Whenever you see this you will get the location of one of the APC's.
It definitely helps if you have your batmobile's weapons suped up a bit, since you have to fire rockets at the APC's while getting attacked by other cars. Also, it can make things easier if you have the ramming ability of the batmobile unlocked. With it you can bump into other cars and make more damage as with the normal afterburner.
All in all this is a very easy achievement and you do not need to worry about it, since intel on the locations will come by themselves after a while. If you happen to just see one on the streets by youself get your car and start aiming to speed things up even more.
The achievement unlocks after you have destroyed the 9th APC.
If you need further help, refer to the video below
(video credit: XxRajeevx x)