British Rail Class 333

The Class 333 was a fleet of sixteen four-car 25 kV AC electric multiple unit sets built between 2000 and 2002 by CAF (Construcciones y Auxiliar de Ferrocarriles) of Beasain, Spain, with electrical equipment by Siemens, ordered by Arriva Trains Northern (and funded by West Yorkshire Passenger Transport Executive) for the newly-electrified Aire Valley and Wharfedale lines radiating from Leeds. The electrification of these Yorkshire commuter routes — from Leeds to Skipton, Ilkley, and Bradford — was completed in 1995–96, and the Class 333 was ordered as the dedicated EMU fleet for the newly-electrified services, replacing the diesel DMUs and locomotive-hauled coaching stock that had previously worked these heavily-used commuter corridors.

The Class 333 was CAF's first major British rail order and represented a significant departure from the BREL York standard that had dominated British suburban EMU construction for two decades. CAF's design featured an aluminium body structure rather than the steel construction of the BREL fleet, giving a lighter vehicle with good corrosion resistance, and an interior specification that reflected the West Yorkshire PTE's investment in attracting commuters out of their cars and onto the newly-electrified rail network. The Siemens electrical equipment used IGBT inverter technology for the traction control, a step forward from the thyristor systems of the BREL Classes 317–321 and one that gave the Class 333 excellent acceleration characteristics suited to the frequent stops of the Leeds commuter network.

Sixteen sets were delivered in 2000–02 and entered service on the Aire Valley electrified routes: Leeds to Skipton via Keighley, Leeds to Ilkley, and Leeds to Bradford Forster Square. The sets carried the distinctive Arriva Trains Northern turquoise and white livery on entry to service before transitioning through the Northern Rail and Northern Trains livery evolutions that followed successive franchise changes. The Class 333s have operated exclusively in West Yorkshire throughout their careers, and the entire fleet remains in active Northern Trains service as of 2026, approaching twenty-five years old but maintained in good condition through regular maintenance and interior upkeep.