Marine Trucks were a type of vehicle that Alex Mercer and James Heller often found trundling along with New York (and in case of Prototype 2, New York Zero) traffic, as easily panicked as a civilian automobile and just as easily destroyed. They were used by the Military to transport Marines around the city and were most often found within a Military-Controlled Zone.
The truck is based on the M939 "5 ton" truck and a modified bed design with additional fencing, it appear in both games but has different look. In Prototype, it has camouflage netting covered while in Prototype 2, it's uncovered.
Oddly, in Prototype, the back of the truck is empty and no Marines are seen inside, despite the fact that they were deployed to transport Marines. However, in Prototype 2, the truck is really carrying Marines and should the player reach an alert status if a Marine Truck is present, the six Marines on board will disembark and will engage Heller. Additionally, Marine Trucks arrive after an alert is caused by the player and should Heller be disguised the Marines will exit to look for him.
The Marine truck is one of the few vehicles seen driving through the Red Zone in Prototype 2, with its occupants in the back shooting at the infected from the back of the trucks. If the vehicle is disabled by infected hitting it, the marines will not dismount and instead remain atop the vehicle, shooting at any infected. However, if Heller is seen, the marines will dismount and will attack Heller.