The Sydney Trains Millennium or M sets are a class of electric multiple unit operated by Sydney Trains in Sydney, New South Wales, Australia. The fourth generation trains entered service from 1 July 2002 after short delays due to electrical defects. The trains can operate over the entire suburban network, but currently only operate on Sector 2.The Millennium trains replaced the aging 1960s Tulloch trailers and provided extra capacity on the CityRail network.