British Rail Class 166 Networker Turbo

The BR Class 166 Networker Turbo was a fleet of twenty-one three-car DMU sets built in 1992 by ABB Transportation at York, representing the higher-specification express variant of the Networker Turbo family developed for Network SouthEast's Thames Valley services. Where the Class 165/0 three-car sets worked the stopping and semi-fast Thames Valley services to Oxford, Newbury, and Bedwyn, the Class 166 was designed for the faster and longer-distance Reading–Oxford and Reading–Paddington semi-fast workings, with a higher interior specification and first-class accommodation.

The Class 166 used the same Perkins 2006-TWH engine installation as the Class 165 but was built to a slightly higher interior specification, with first-class seating in one vehicle of each three-car set and air conditioning throughout from new. The wider Networker body profile (2.82 metres) and the three-car formation gave a comfortable and spacious environment well suited to the Thames Valley business commuter market that NSE was targeting.

The twenty-one sets entered service in 1992 on Thames Valley semi-fast and express services out of London Paddington. Under privatisation they passed to First Great Western and subsequently Great Western Railway, working the Oxford corridor alongside Class 165 and, later, Class 800 Hitachi bi-mode sets. As of 2026 the Class 166 remains in service with GWR, though cascade to secondary duties has begun as newer rolling stock takes over the principal Thames Valley workings.