Overview

The T21, introduced in the 1950s and originally designated T2, is a diesel-hydraulic locomotive that served Sweden's state railways and several private lines. Developed from a German prototype family related to the Deutsche Bundesbahn's V65, the T21 was built through a cooperation between Maschinenbau Kiel (MaK) and Svenska Järnvägsverkstäderna. About sixty locomotives were delivered in the 1950s to meet a need for reliable, economical traction on secondary routes and branch lines where steam had been dominant until then.

Design and construction

The T21 combined a medium-power diesel engine with a hydraulic transmission. This pairing was selected because hydraulic transmissions provide smooth power transfer at the low speeds and frequent start-stop work typical of branch-line services and shunting. The basic mechanical layout and components were closely related to the MaK 800D family; the Swedish deliveries included adaptations to local operating practices, braking systems and crew accommodations.

  • Role: branch-line passenger and freight, light shunting
  • Drive concept: diesel engine with hydraulic transmission
  • Builders: Maschinenbau Kiel (MaK) and Svenska Järnvägsverkstäderna
  • Era: built in the 1950s and used through the late 20th century

Transmission variants and the T3/T22 experiment

Within the production run SJ experimented with a domestically produced hydraulic transmission. Locomotives fitted with that Swedish transmission were initially classed as T3 and later redesignated T22. The locally made shift proved less satisfactory in regular service than the proven German units supplied by MaK, and only a few of the Swedish-built transmissions entered service. Some of those units were subsequently converted to the standard specification to improve reliability and maintainability.

Production and operators

SJ's original order covered the bulk of the series, but additional units were sold to private operators. Nora Bergslags Järnväg (NBJ) purchased a small number of T21s in the early 1960s to modernize its fleet for mixed traffic on regional lines. The cooperation between German and Swedish workshops meant the series combined imported expertise with local assembly and finishing, a common practice in post‑war European locomotive procurement.

Operational use

The T21 replaced many steam locomotives on lighter duties: branch-line passenger trains, short freight turns and yard duties. Operators valued the class for its operational flexibility, lower fuel and maintenance demands compared with steam, and the ability to be run by smaller train crews. The locomotives performed well where axle load restrictions and lighter track prevented the use of larger mainline diesels or electrics.

Withdrawal, preservation and legacy

As traffic patterns changed and more lines were electrified or closed, the T21 fleet was gradually withdrawn through the 1970s, 1980s and into the 1990s. Several examples have been preserved by railway museums and heritage societies, where they are sometimes still used on special services or displayed as examples of Sweden's mid-century dieselisation. The class is often cited in technical histories of diesel-hydraulic locomotives and in discussions of the modernization of Statens Järnvägar.

Technical and historical context

The T21 project illustrates wider trends in post‑war European railways: a move away from steam, adoption of diesel traction for secondary services, and collaboration between established manufacturers and national workshops. Its story is closely connected to developments in transmission technology and to the differing operational philosophies that favoured diesel-hydraulic solutions in some countries and diesel-electric in others. For background on the types of motive power the T21 replaced, see materials on steam locomotives and the nature of branch lines as a railway category.

Further notes

While the T21 never achieved the iconic status of some mainline locomotives, its contribution to everyday regional rail services was significant. Preservation examples and contemporary photographs help document variations in livery, minor rebuilding work and the operational contexts in which these locomotives worked. Enthusiasts and historians researching mid‑20th century Swedish traction will find the T21 a representative case of export-derived designs adapted for national needs.