Unidentified boarding craft
From Halopedia, the Halo wiki
When a UNSC ship is being attacked by Covenant forces, if the Covenant determine that the ship holds valuable navigational data, AIs, or other materials, the Covenant may attempt a boarding operation. In such a situation, the boarding craft is used. So far, the Covenant have proved highly intelligent in their entry points, having burnt holes through hangar bay windows or used the empty UNSC escape pod docking rings to board a vessel. These craft were only viewed partially and internally with only the boarding tube being accessible and the cockpit being off-limits behind a locked door. These vessels usually carried a compliment of up to 8-10 Covenant warriors, usually Unggoy and Sangheili.
In Halo: Combat Evolved, they contained two Overshield power ups in the far corners of the pods, probably put there for the use of any Sangheili in need of assistance that were on board.
List of appearances