As with the other DLCs, you need to beat only Volume 3 on Mein Leben difficulty to get the achievement. This is easily the easiest of the Mein Leben achievements. Thanks as always to Kreeper V for leading the way. I adapted his strategy outlined in his video:
Very general strategies:
* 1st commander area: kill the one guard and commander on the way to the exit.
* 2nd commander area: it's hard to avoid raising the alarm. Plus, you'll want the dieselgewehr for commander area 3 anyway. So use the chokepoints at the top of the stairs and on the ground floor to funnel enemies towards your shotguns.
* 3rd commander area: you're in a cramped hallway with an explosive weapon. Go to town. You should have just enough ammo to take care of everyone. If you run out, you have your shotguns.
* Ballroom: Stay up on the vents and do your best to stay stealthy. Only go for headshots when you're confident, especially when killing the dog. I've found that body shots end up raising the alarm, since everyone's already on high alert. You'll know it's safe to jump down when the general says some dialogue about getting to the bridge.
If you do raise the alarm, you can head back to the vent and grenade the crowd that gathers below.
I recorded a messy run, so you can see how to adapt to the reinforcements: