The SS3 or Shaoshan 3 is a six-axle freight locomotive developed by the Zhuzhou Electric Locomotive Works, utilizing advancements in electronics which have been made in the seventies. While it was still mainly controlled by a tap changer, thyristors were used for fine adjustment between the steps. The prototype was completed in 1978, but series production only started in 1986. The main characteristics were a top speed of 100 km/h, a starting tractive effort of 470 kN, an output of 4,800 kW and 4,000 kW in dynamic braking. After a total of 677 had been produced in Zhuzhou, Datong and Ziyang, production switched to the 4000 series in 1991. This had full thyristor control, improved bogies and an advanced anti-slip control. By 2007, 733 locomotives of the 4000 series had been produced and also most of the original series had been rebuilt. Between 2002 and 2011, 360 two-section locomotives were built as SS3B. These can haul 10,000 tonnes at 54 km/h on an incline of 0.4 percent, or 4,000 tonnes at 50 km/h on 1.3 percent.