Rolling Thunder
Ultra rare0.8%ObjectiveOptionalSingle-player
Operated four different vehicles at once in Mission 13 on Heroic difficulty.
Mission 13 (Reclamation) is the big vehicle battle. You need four different vehicle types being operated at the same time - realistically a 4-player co-op run where each Spartan grabs a different vehicle (Scorpion, Wraith, Ghost, Warthog/Mongoose) simultaneously in the open battlefield. Solo you'd be relying on AI teammates crewing vehicles alongside you, so co-op is far cleaner. On Heroic, though the difficulty isn't the hard part here.