Pushing the Payload

Relatively simple achievement this one.

During the World Quest 'Stack on the Tank', which spawns during a Zuldazar assault, a progress bar will fill up as you escort the tank along the path. Before the progress bar reaches 100% and the quest completes, you must kill 6 of any combination of Warbound Rearguards or Warbound Raiders which will spawn around the area. I was able to stand directly under the tank and taunt enemies to me and kill them. I'm not sure if you need to be directly under the tank or just close enough to get credit for the progress bar, but just to be safe I stayed under it at all times.

Edit: If the World Quest 'Crate 'n' Barrel' isn't up, you may struggle to kill enough enemies before the progress bar fills up. There a two solutions to this; you can form a group via the premade group finder and convert to raid (this will prevent you from completing the quest but will still give you the kills needed for the achievement) or you can actually pull ANY enemy to you and kill that as it's been confirmed that any killable creature counts towards the achievement, not just the spawns (whether or not this is intended is unclear for now). Thanks to the comments for these two tips.

Hope this helps and good luck o/

This achievement is apparently lifetime cumulative, and not on a per-WQ basis. I did this world quest back when assaults were new and before I had looked at the achievements, and therefore did not get it. I just did the world quest now, and earned the achievement upon killing my first mob.

Critters count.