Overview

The British Rail Class 28, originally marketed as the Metropolitan‑Vickers Type 2, was a family of diesel‑electric locomotives built for British Railways as part of the postwar Modernisation Plan. Intended to provide medium‑power traction for mixed traffic duties, the class stood out chiefly for its unconventional wheel arrangement and distinctive mechanical choices. They were one of several experimental designs produced in that era as British Rail sought to replace steam traction and evaluate new diesel technologies in service.

Design and characteristics

Class 28 locomotives combined a diesel prime mover with electric transmission to the axles. The most notable feature was the Co‑Bo wheel arrangement: a six‑wheel bogie at one end and a four‑wheel bogie at the other. The six‑wheel bogie provided three driving axles while the four‑wheel bogie contributed the remaining two driving axles, producing five driven axles in total. Many performance attributes flowed from this layout.

  • Wheel arrangement: Co‑Bo, creating unequal axle loading between ends.
  • Traction: High starting tractive effort for a medium‑power locomotive, aided by five driving axles.
  • Role: Intended for mixed traffic and secondary passenger and freight workings.

Operational history

Introduced during the transition away from steam, these locomotives entered a railway environment that was testing many new types simultaneously. The Co‑Bo design was unusual for British practice and required careful route selection because the different axle loads limited availability on some lines; this concern is often discussed under the subject of route availability. Similar asymmetric arrangements were not unknown internationally, and there are comparisons with examples used in countries such as Japan.

Technical and maintenance implications

The asymmetry of having a six‑wheel bogie at one end and a four‑wheel bogie at the other complicated maintenance routines and depot allocations. While the locomotives delivered an unusually high maximum tractive effort for their power class, the mixed axle loads demanded careful attention to weight distribution and track forces. Their mechanical and electrical systems were notable examples of experimental mid‑20th century diesel engineering; they were part of the broader trend of learning which features would become standard and which would not.

Uses, examples and comparisons

In service the class performed duties on secondary passenger trains and freight turns where their tractive characteristics were useful. As with many experimental classes from that period, their operational record helped inform future design choices: the value of standardisation, the trade‑offs between adhesion and axle loading, and the practical costs of non‑standard parts. Discussions of diesel locomotive development often cite the Class 28 as an instructive case of innovation paired with limitations.

Distinctive facts and legacy

Though not typical of later British mainline designs, the Class 28 remains remembered for its Co‑Bo layout and the lessons it offered engineers and operators. References to the type often use the manufacturer name and model, such as Metropolitan‑Vickers Type 2, and contemporary accounts classify them simply as diesel locomotives. Technical analyses and preservation notes frequently point to the balance between the high starting tractive capacity and the practical constraints imposed by asymmetrical axle loading. For comparative study and historical context see specialized sources and fleet lists that document locomotive experiments of the Modernisation era, including practical comparisons with asymmetric designs used overseas such as those mentioned on Japan and other networks. For more technical background and preserved examples, consult further reading and archived engineering reports available via dedicated railway heritage resources (bogie design), (tractive effort) and operational assessments (route availability).