English: SWT Classes 444 and 450 at London Waterloo on 21st August 2007. Both classes belong to the Siemens Desiro UK family of multiple units. SWT ordered the Desiro Units from 2003 to replace the Mark 1 slam-door EMUs which it previously operated. Many Mark 1 EMUs in SWT's fleet were more than 40 years old, and they did not meet up with modern health and safety requirements. Therefore, all TOCs were required to replace their Mark 1 rolling stock with new trains. The Class 444 is used primarily on express services from London Waterloo to Weymouth, Portsmouth Harbour, Haslemere and Poole, but is also used on some outer suburban services to Alton and Basingstoke. The Class 450s were built for use on outer suburban services to Weybridge, Reading, Alton, Basingstoke and Windsor and Eton Riverside, but are also used on services to Haslemere, Portsmouth Harbour and Poole, and to a lesser extent on services to Woking, Guildford (via Cobham or Epsom), Dorking, Chessington South, Hampton Court, Teddington, Shepperton, Strawberry Hill and Hounslow.