The new D-Series Unit Rig model integrates a Cat 3516C HD engine and the Cat 240T AC electric drive system with the existing Unit Rig MT4400 to create the MT4400D AC. The new truck, with 2,500 net horsepower, has a rated payload capacity of 240 tons and a rated gross machine weight of 865,000 pounds. The MT4400D AC features dynamic retarding capacity, combined with rear wet-disc brakes. The truck’s drive train, says Caterpillar, also leverages the experience of Electro-Motive Diesel (a Caterpillar company) in inverter design and manufacturing.