Space Hulk: Tactics

I missed this achievement when I first played the genestealers campaign.

On mission 2 - “Ultramarine Counterattack”, make sure you select the mission that has “protect the consoles” as it’s secondary objective

Finish the mission (you need to kill the plasma heavy weapon) and the achievement will unlock.

Good luck!!

After a few failed attempts, I tried the strategy in Jet R's video and got this on the first try in the second Genestealer mission where you have to defend both consoles and/or defeat the Plasma Cannon Heavy Weapon Bearer, either in 20 turns or less.

Basically, you just keep spawning in the spawn point above the Ultramarines' spawn point, and try to catch them in the first room to THEIR right of THEIR spawn point (emphasized for perspective purposes). While you keep spawning Genestealers to approach from the Ultramarines' right-side, also move your Bulwark Biomorph as close as possible to force the Ultramarines to choose a side to engage. I got lucky and snuck a Genestealer across the room past the Sergeant's overwatch (three whole overwatch squares, got REALLY lucky!), and parked next to the Plasma Cannon Heavy Weapon Bearer face-to-face, attacked him from the front and got him on the first attack, achievement popped during the attack cutscene!

Here's Jet R's video: