Doozy

The Doozy was an UNSC vehicle that didn't make it into Halo: Combat Evolved or Halo 2, and is seen in the Halo 2 Collector's Edition Video. It ended up getting a chaingun in the back, and to man the chaingun, one had to sit in the "nause seat", which faced backwards.

Interestingly, in the Halo Editing Kit, there is an option for vehicle types, and one is 'human boat.' This is because Bungie had built in a boat function into the game engine, but the concept was never used.

The Halo Encyclopedia lists a vehicle of the same name which it describes as a modified snowmobile, used for quick movements over snowy ground, particularly for medical transport, messaging, diversionary tactics, and evacuation. Its physical descriptions is otherwise essentially the same as the boat version, noting that the "nausea seat" proved to more of a hindrance than a help. The Doozy is the only vehicle based on deleted material featured in the Encyclopedia.