[Paul]

http://halo.wikia.com/wiki/Spirit

The Spirit, otherwise known as the DX-Class Dropship, is a Covenant troop aerial transport vessel primarily seen in Halo: Combat Evolved. They are angular, tuning fork shaped craft with two parallel personnel bays along the exterior of each "prong". The Spirit is used by the Covenant alongside Phantom dropships. They are used to transport Elites, Jackals, and Grunts, and have been known to ferry Covenant vehicles within the purple colored energy field between it's prongs. Around the time of The First Battle of Earth it would seem that the Spirits were replaced with the more heavily built Phantom dropships.

It is speculated that the Spirit is not designed for combat drops. That particular job is for Phantoms. The lack of effective offensive or defensive weaponry coupled with the small troop carrying capacity of the Spirit tends to support this supposition. Since the fleet stationed above Halo was originally a research operation this use of non combat specific transportation would be understandable. During the events of the Battle of Installation 04 Spirits were placed into combat roles by necessity.