Iris standing at Idreghay station

"Iris the railcar"

M79900's driving cab

Derby Lightweight-M79900-Iris

British Railways were a late starter in introducing diesel railcars. They had observed other countries experiences for several years before the Railway Executive announced a £500,000 programme in November 1952 to introduce eight lightweight units to the West Riding of Yorkshire. They were designed by a team headed by R.A. Riddles, first Chief Mechanical Engineer of British Railways. The units were intended to undergo a testing period before being built en-mass as the standard for use throughout the country. Long before the first vehicles were complete though it was announced in September 1953 that the scheme would be extended to include the West Cumberland area, and to many other areas announced in February 1954. This was entirely typical of the period, a mad rush to modernise the railway resulted in a huge variety of locomotives and other vehicles being commissioned and their “test” batches being extended into bigger productions runs before they were properly tested, resulting in some wretched designs, though the Derby Lightweights were largely successful.


In all 219 vehicles were built in 1, 2 and 4 car formations. The first entered service in June 1954 in West Yorkshire. Built originally as a 2-car set, 79900 was converted to a single car shortly after being built to allow it to operate on the Branch line from Bletchley to Buckingham. The Derby Lightweights met with huge success, starting a trend of greatly increasing passenger figures which most first generation diesel railcars continued. The livery was engine green, though a very few survived long enough to be repainted in rail blue, but not 79900 which became a departmental unit for use as a test car for survey work, such as that for the Radio Electric Token Block (RETB) signalling system. This is where the vehicle gained the name Iris, during which time it was painted in the Research Divisions red and blue livery and based at Derby RTC.


Derby Lightweights were considered non-standard due to their Yellow Diamond coupling code (most other first generation DMUs to be built from 1956 were Blue Square) so they were destined for early withdrawal, with the last withdrawn from passenger use as early as 1969.

A single car and a 2-car went into departmental use, thankfully keeping them long enough to enter the DMU preservation era. These are the only survivors of the 219 built. 79900 was beautifully restored at the Midland Railway Centre, Butterley and arrived with us after a brief spell at the Churnet Valley Railway in Staffordshire. As the flagship of the preserved railcars in the country, the vehicle has also visited gala events at the Llangollen Railway in Wales as well as the Severn Valley Railway since it has been in our care. The vehicle has the highest rating of 1 from The Railcar Association meaning that the preservation and care are of paramount importance, being now the oldest of the operational first generation DMU's remaining.

Iris the Railcar is a unique historically and locally significant vehicle and runs on a regular basis for the general public and enthusiasts alike to enjoy. Be sure to visit the railway for a ride on this beautifully restored vehicle. We regularly post which vehicles are operating services on Facebook so be sure to 'like' us to find out when Iris is running!

Seats: 52 second class
BR alternative number: ADB975010