I noticed on the recent Halo Bulletin that down where the Operator section is is says that it can be used in vehicles in space, air, ground, and sea.
-Operator Specialization: Spartan optimization for the operation and control of a wide-range of vehicles; space, air, ground, and sea.-
Notice that at the end it says SEA. Could this be a hint that in Halo 4 we get to drive in water transport vehicles such as boats and such? I dont know if there has been any mention on it but if anyone hadnt noticed or thought about it there it is.