The maintenance, repair, and modification of heavy-duty vehicles and mobile equipment which have utility systems or special hydraulic, pneumatic, mechanical, electrical, or electronic systems, features, or controls designed for such purposes as construction, combat, earth moving, ship loading, firefighting, and comparable industrial or special applications. Examples of heavy-duty equipment covered by this series include bulldozers, road graders, crawler tractors, power shovels, locomotives, combat tanks, cranes, large missile transporters, and fire trucks. The repair of major systems (such as diesel, gasoline, multifuel, and turbine engines; automatic, standard, and cross-drive transmissions; heavy duty drive line systems; and hydraulic, electrical, and mechanical utility systems) is included, whether accomplished as part of or apart from repair of the total piece of heavy mobile equipment involved. The work requires knowledge of how heavy-duty machinery, engines, parts, and systems work; ability to detect faulty items, determine causes of malfunction, and determine best repair methods; and skill to assemble, disassemble, repair, or modify components and systems.