The Derricks are vehicles created by the COG (Coalition of Ordered Governments) to help them travel into the Locust tunnels using the Grind Lift. Basically, the Grind Lift drills onto the ground, allowing the COG into the tunnels. The Derricks also have weapons aboard to help fight off the Locust Horde, which are the Chain Guns. The Chain Gun is identical to the Troika. You can see the Derrick on the Gears of War 2 Gameplay Video. Dizzy Wallin, one of the pilots of a certain Derrick, calls his Derrick "Betty."