The British Rail Class 442 Wessex Electric (or 5WES) electrical multiple units were introduced in 1988 on the South Western Main Line from London Waterloo to Southampton Central, Bournemouth, Poole and Weymouth. Twenty-four of these 5-car units were built in 1988/89 by BREL at its Derby works. Their introduction coincided with the completion of electrification from Bournemouth to Weymouth.