Covenant air artillery
From Halopedia, the Halo wiki
The Covenant Air Artillery is an airborne vehicle armed with three plasma mortar]]s (the main armament of the Wraith) and its a sort of airborne seige vehicle for raining plasma down upon UNSC bases and destroying them. Below is a exceprt of information on it.
"Covenant Air Artillery have recently been sighted behind several front line battles, it seems that the Covenant have developed an air based artillery unit. With no on board defenses, it can be very vulnerable if dealt with promptly. However, its heavy plasma mortar cannons can lay waste to an entire UNSC base quickly and it is therefore critical that we gain more field information on this vehicle." [1]