This is very simple to get at the start of the mission, and only requires that each Spartan be in any vehicle, but there can only be one Spartan per vehicle.
Get everyone in the scorpion and head down the ridge to find two ghosts. Blow one up and then get out of the scorpion and hi-jack the other one. Then bring it back up the ridge to find two more parked ghosts along the edge. Use the d-pad to command your team to get into the three ghosts and then you get in the tank. This will pop the achievement.
Video guide can be found here: