At the dawn of the 1990s British Rail commissioned two DMU classes that would go on to live long lives along major routes in the south of England. The Turbos, as they would come to be known, began with the Class 165 used by both BR and the popular Network SouthEast brand as part of their Chiltern operations. But later the need for a faster, express version was apparent and from '92 the Class 166 was produced to fulfil this role. 30 years on and the 166 is still moving passengers in England's southern reaches, both in and around the capital London and more recently around the southwest into Bristol, Somerset and Devon.

The 166's most notable advantage over its visually similar predecessor is its increased top speed - being able to run at 90 mph rather than the 75 mph limit of the Class 165. This was useful particularly for its operations out of London Paddington, whizzing passengers out along the Great Western Main Line to Reading and beyond to Oxford and sometimes Banbury. Initially their services were referred to as Turbo Express but later variants of this term were used to refer to the units themselves including Networker Turbos or Thames Turbos the latter of which it has shared with the 165s.

The Cotswold Line also saw 166 services head through to destinations in Herefordshire and Worcestershire, though in the main their home remained along the busy Thames Valley. After privatisation under the First Great Western and then GWR brands these services continued whilst the Class 165s served the branch lines to places like Windsor & Eton, Henley-on-Thames and Marlow.

The most recent significant change in the Class 166's operations came with the move of some units to St Philips Marsh, Bristol in 2017. This saw them frequent services across Somerset and Wiltshire, even making their way into Devon where their express ability was an advantage over other classes outside of the modern IET and iconic HST sets. This hasn't restricted them to main line work however with an occasional 166 making its way to Okehampton and the newly reopened Dartmoor Line as well as the Barnstaple Line which winds its way through to the north Devon Coast.

These important DMUs have thus made a mark on many-a-railfan familiar with the southwest and trips along the GWR to London. Their 30 years of operation under numerous guises and along a variety of lines has seen them appear at stations across the region and with their scope expanding even in recent years, there's no telling where they might end up next.

Experience operating the Class 166 between London Paddington and Reading with the Great Western Express add-on for Train Sim World 2 on PC and Console: Steam Store

Find out more about the most recent update to Great Western Express here

Or check out last nights Railfan TV 4 UP challenge here, in which 4 of the Preservation Crew team explore the route and discuss the update in detail.