Spoiler Alert:
This is a MAIN story related achievement. You get this for taking the Arkham Knight's Cloudburst tank out. Towards the end of the campaign the Arkham Knight and Scarecrow will disperse the cloudburst through the cloudburst tank controlled by the Arkham Knight. The city will become engulfed in an orange cloud (lower street levels) and you will be tasked with finding the Arkham Knight's cloudburst tank on Bleake Island. Once you stumble upon it this turns into a boss fight with three separate stages.
Stage 1: Eliminate the 6 Cobra tanks, this is done exactly have you have dispatched all the others by simply sneaking up behind them and shooting them in the back. As there is 6 and vision is at a minimal I advise playing tactfully and waiting until one is off by it's lonesome before taking it out, then quickly vacating the area once you have destroyed it.
Stage 2: Once all 6 are destroyed you will face the Cloudburst tank one-on-one, this tank has 4 key areas to shoot (after some dialogue with Alfred you will know which areas these are and your rocket will lock-on like with the Cobra tanks). After every hit you want to get as far away as quick as you can because this tank is VERY fast. Rinse and Repeat.
Stage 3: Now for me this was the easiest stage, simply lay into him with all you have got (aim for the orange glowing bit on the back of the tank for more damage). He will shoot homing missiles (shoot with the vulcan cannon), rockets with that laser sight (boost away and lose LOS) and AOE (area of effect missiles) avoid the red patches on the ground.
Defeat this tank and bang, the achievement is yours.