D96-TCE Albatross
From Halopedia, the Halo wiki
The Albatross transport is a very large dropship that is probably capable of holding about four times as much cargo as the Pelican dropship. It is usually used to drop vehicles and UNSC personel en masse to a site. When dropping its cargo, 3 sides of the cargo tray open up to allow vehicles and personel to leave the cargo tray.
Appearances of the Albatross
The Albatross is visible only as a concept in the book The Art of Halo. However, the cargo tray of the Albatross is visible on the Halo 2 multiplayer map Relic, where it is crashed on one of Relic's beaches. In Relic, the rear section of the cargo bay is open, and a Warthog can be seen on a ramp leading to its innards. Although there is only one Warthog, the rear's interior looks large enough to fit 6 Warthogs, or a couple of Scorpion Tanks.
Another theory, although less prevalent, is that the Albatross could be a mobile command post. It is used as such on Relic, being the base for one of the teams. It may also be able to perform transport and command post roles alternatively, switching between the two.
There was also a dropship in the Halo Wars trailer which is, by some, presumed to be the Albatross.
