During the last Invasion we received a number of tickets about the Rocket Silo in base failing to fire on enemy units during defensive battles. In the majority of cases players referred to the Achilles GS as the rocket which was failing. We have run a number of tests with the QA team and found that both the Achilles and Achilles GS are working correctly. We have found that in most cases the issue is caused by a bit of confusion surrounding the different targeting rules for those two rockets.
Targets LIMITED units - that includes all Special Forces, Hero units and all Unique units. Any unit which you cannot have more of than you have unlocked in the past.
Targets Unique units - This only includes units which are True Unique units you can tell these units from others because when you check the research or production buildings. You will see a Diamond Icon like this one:
What about the Herald?:
The Herald is a unique unit, However only Pure AA units can target it, because it is also a High Altitude Air Unit. Since the Achilles GS will also target ground based unique units like the Juggernaut or War Rig it will not target the Herald. High Altitude units are signified by this icon:
What about Heroes:
Hero units are limited, but they are not True Unique units. The hero designation will be represented in the game with this icon: