UNSC Vehicle Depot
From Halopedia, the Halo wiki
The UNSC's Aircraft Pad's ground based variant. It appears to (quickly) manufacture it's vehicles undreground and transport them to the surface via a movable ramp. Capable of building and reinforcing the UNSC's powerful ground based Corps with Warthogs, Wolverines, Rhinos, and Scorpion Tanks.
Refernece
http://forums.halowars.com/forums/1/91352/ShowThread.aspx#91352