79900 Iris

79900 is a Derby Lightweight Driving Motor Brake Second, part of the pioneering first-generation DMUs introduced in the 1950s to modernise Britain’s branch lines. Known for their lightweight design and economy, Derby Lightweights were an important step in replacing steam services and improving regional rail travel.

After withdrawal from national service in October 1967, 79900 avoided scrapping through conversion into “Test Car Iris.” Preservation began in 2000 at Midland Railway Butterley, where it underwent a full rebuild by 2004. This extensive restoration included reconstructing bulkheads, installing new Formica panelling, and fitting seats salvaged from a Class 101. The mechanical overhaul involved a complete refurbishment of the bogies and drivetrain. Relaunched in late 2004, 79900 quickly gained recognition as one of the finest preserved early DMUs.

Originally built with the distinctive Derby Lightweight “Yellow Diamond” multiple working system, this was replaced during preservation with the more common “Blue Square” system, allowing 79900 to operate in multiple with most other DMU types. To maintain historical accuracy, the original Yellow Diamond sockets were restored as dummy units on the cab ends. Additionally, the original Derby Lightweight controllers were missing, so the cab was adapted to use standard DMU controllers. Accessibility improvements include a modified brake van area that creates a small rear saloon suitable for wheelchair access.

Between 2000 and 2007, 79900 was based at Midland Railway Butterley before moving to the Churnet Valley Railway briefly. It then spent nearly 14 years at the Ecclesbourne Valley Railway, where it regularly ran and earned great popularity. During this time, its seating was upgraded in 2011 to original high-backed Derby Lightweight seats complete with chrome handrails and authentic early BR green upholstery.

79900’s active preservation career includes visits to several other heritage lines, such as the Llangollen Railway for gala events in 2008 and 2017, the Severn Valley Railway for the Railcar Reunion in 2010, and the Dean Forest Railway, which hired the vehicle in 2016 and again in 2022 to mark 30 years of DMUs on that line.

In 2014, after a decade in preservation, 79900 was repainted and returned to traffic quickly. It also took part in a charity event in Derby, hauled by a Network Rail team. Repairs were carried out later that year to fix a blown cylinder head gasket.

The Covid-19 pandemic temporarily halted visits, but 79900 resumed travel in 2022, including participation in the Railcar Association convention weekend at the Great Central Railway, where it remains operational.

In 2025, 79900 featured at Alstom’s “The Greatest Gathering” works open day at Derby Litchurch Lane, joining other Derby-built DMUs in a heritage showcase.

Today, 79900 continues to operate regularly on the Great Central Railway, serving as a remarkable and well-loved example of the early generation of British diesel multiple units and preserving the legacy of Derby Lightweight engineering.