From Halopedia, the Halo wiki
Warzone Assault retains many similar mechanics to the standard Warzone gametype, though notably features no AI enemies. In this variant, one team is tasked with defending the bases on the map while the other team attempts to capture each base and push the other team back. The defending team must hold each base until a set time limit runs out. If the attacking team manages to capture a base, they force the defending team back and extend the timer. If all bases are captured the attackers must assault the defenders' home base and destroy their core to win.
The REQ system acts the same as it does in normal Warzone matches, except that the speed of progression through the REQ levels is accelerated due to the gametype's faster nature. Winning by earning 1000 VP is not possible in Warzone Assault, and there are no AI enemies in Warzone Assault, save for the defender's Marines.
Warzone Assault maps are typically remixes of normal Warzone maps, though those added in downloadable content updates to Halo 5: Guardians were designed from the ground-up to be Warzone Assault maps.
Unlocks and rewards
Warzone Assault uses the same medals, commendations and unlocks as the regular Warzone gamemode, which can be viewed here.