Missile silo
From Halopedia, the Halo wiki
The UNSC Missile silo is a building that houses a missile launch bay in the game Halo Wars. According to the Halo Wars preview, most UNSC bases have at least one, sometimes more. The warhead looks like it's either nuclear or a very large conventional one. It is likely that the missile is a "superweapon" for the UNSC, as "superweapons" are found in many RTS games.
It may be related to the 11-B1 ICBM, the launch silos that populate the landscape on the Halo 3 map Standoff.
