From Command and Conquer Wiki

The Weapons factory (also termed "War factory") was designed to produce GDI armor for the First, Second, and Third Tiberian Wars. The Weapons Factory consists of a central manufacturing area where the construction process of the unit takes place. A collection of robot welding arms, a smelter, and several other equipment related to the manufacturing of parts for the assembly are here too. They can in effect rapidly construct combat vehicles from "knocked down" versions in storage.

During the Firestorm Crisis, the Weapons Factory was mobilized; the GDI Mobile War Factory and Nod's Fist of Nod, although these units were extremely slow. Also, due to their new design, they were only able to be produced one at a time. By the Third Tiberium War the factories and the Warp Spheres have repair drones to heal units.

For a list of units that could be produced by the factory, examine the list of units constructed in the war factory

Global Defense Initiative Third Tiberium War Structures

Buildings Construction yard · Tiberium refinery · Barracks · War factory · Command post · Airfield · Armory · Technology center · Space command uplink Aux. structures Tiberium silo · Watchtower · Guardian cannon · AA Battery · Sonic emitter · Ion cannon control · Battle Base