From the beginning of the mission, quickly get in the Spectre and go inside the building. Follow the hallway, enter the large room, and then desend using the right hand side ramp. In the very corner of this area, next to the cliff side, you'll see a Scorpion (tank). Get out of your spectre, and press the board to board and hijack this scorpion. Use melee to kill the enemy inside without blowing it up. Once the enemy is dead, unboard it, then board it again to get inside the tank and the achievement will unlock.