Mortardom Achievement in Halo: The Master Chief Collection

The first order of business here before attempting this achievement is to successfully hijack an enemy Wraith. The best way in doing so would be to pick off a Wraith’s turret gunner from afar with a ranged weapon, and then shooting an overcharged Plasma Pistol shot to immobilize the vehicle. With the vehicle immobilized, you will now want to quickly jump into the turret gunner seat. This will force the driver out of the cockpit, so get ready to mow down the pilot with the turret and the Wraith is now yours.

With this in mind, load up Rally Point Bravo on the mission in question and proceed through the canyon and through the Forerunner structure until you take a portal that links you up with your Marines. It's worth noting that during the canyon fight, you should grab a Plasma Pistol. Once you are grouped up with your Marines, hop inside one of the Scorpion tanks and kill your allies and the Covenant Ghosts in the area.

Now you can safely pick off the gunner of the Wraith straight ahead, Plasma Pistol overcharge the vehicle, and grab it for yourself. There a total of six or seven enemy Wraiths in this area, so killing four shouldn't be a problem. Once four enemy Wraiths have been destroyed via your own, this achievement will unlock.