Twenty one three car diesel multiple units were built by ABB (York) for Network SouthEast in 1993, just prior to privatisation. they are to the same exterior design as the Class 165 units but were built to a highjer specification which included air conditioning, faster acceleration and a top speed of 90 mph. Built for the company's express services to and from London Paddington they replaced locomotive hauled stock and first generation multiple units to Padington - Oxford and Newbury/Bedwyn services.
Part of the 'Networker' family of diesel and electric multiple units, they feature welded aluminium body shells. They were delivered in Network SouthEast livery but following privatisation they passed to Thames Trains. In April 2004 Thames Trains passed to First group who operated it as First Great Western Link pending the awarding of a new Greater Western franchise. Initially these units retained Thames Trains livery with First Group branding applied ove the Thames Trains logo. The Greater western Franchise was awarded for ten years from 1st April 2006. It comprises the former Great Western Link and Wessex trains operation and was retained by First Group after competitive bidding.
These units continue to operate the services for which they were originally produced for. They also work on Cotswold Line services to and from Evesham, Hereford, Great Malvern and Worcester.