Missile silo
From Halopedia, the Halo wiki
The UNSC Missile silo is a building/weapon 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 11B1 ICBM, the launch siloes of which are part of the Halo 3 map Standoff.
