Tour Coming Through
It is worth 30 Gamerpoints.
Play as any Covenant leader and build ten Ghosts or Choppers, depending on your leader. Move your leader out into the field and use the transporter to send them to your leader. Reselect all your vehicles and then send them back through the transporter from their current position. They will head back to base and through the transporter again. Repeat this three more times and the achievement will unlock as the game tallies the number of units transported.