Gun tower
In addition to the standard features found in all Towers, the Gun Tower is equipped with two Phalanx Wall Turrets on the roof walkway, greatly increasing their tactical value, and providing reasonably robust defence against Infantry or Vehicular assault.
(Note: While a Facility expends NTU to auto-repair Wall Turrets, a Gun Tower is considered to have infinite NTU for this purpose, although the rate is still very slow.)