Unlike Alex Mercer, who had to consume military personnel in order to gain knowledge of how to use the various weapons, Heller can use a variety of weapons attached to vehicles due to his military training. During the escort mission where Heller first finds Roland, you can pick up a vehicular weapon later in the mission. When this is done, one of your fellow escort men will ask Heller if he lifts much, to which Heller replies by stating that he eats a lot of protein.