British Rail Class 122
The BR Class 122, universally known as the Bubblecar, was a class of twenty single-unit diesel multiple unit vehicles built in 1958 by the Gloucester Railway Carriage & Wagon Company. Unlike the two-car and three-car DMU sets that worked most BR branch and secondary services, the Class 122 was a self-contained single vehicle — a powered driving car that could operate alone or couple with other DMU vehicles — designed for the very lightest branch workings where even a two-car formation would be uneconomic.
Each vehicle was powered by two AEC 150 hp diesel engines mounted beneath the floor, driving through a mechanical transmission. The single-car format, with a driving cab at each end, meant the unit could be turned simply by the driver walking to the other end at the terminus — no run-round or turntable required. The Bubblecar nickname came from the distinctive rounded ends and compact dimensions that gave the vehicles a slightly bulbous appearance alongside conventional coaching stock.
The twenty vehicles entered service across several BR regions in 1958, working the most lightly-used branches where their economy and flexibility gave them an advantage over locomotive-hauled trains. They proved popular with operating departments and remained in service through the 1970s and 1980s, some lasting into the early 1990s. Several survive in preservation on heritage railways.
Design and development
Gloucester RC&W built the Class 122 to a BR specification for single-unit branch operation. The two underfloor AEC engines and mechanical transmission followed the standard first-generation DMU pattern, scaled down to single-car format. The vehicles could couple and work in multiple with other first-generation DMU vehicles when additional capacity was required.
Service and withdrawals
The Class 122s entered service in 1958 and worked lightly-used branches across several regions throughout their careers. Their flexibility and economy kept them in use well into the 1980s; the last examples were withdrawn in the early 1990s. Several passed to heritage railways.
Identification features
Single-unit DMU with two AEC engines.
Numbers and names
0Numbered W55000–W55019 (Western Region allocation)20 vehicles; numbered in the 55xxx series.
Notable locomotives
- Several preserved on heritage railways
Allocations and regions
Initially distributed across Western, London Midland, and Scottish regions for light branch working. Concentrated on the Western Region through their later careers.
