The 450 Class is a type of diesel multiple unit (DMU) passenger train formerly used by Northern Ireland Railways.

A total of nine three-car trains were constructed by British Rail Engineering Limited between 1985 and 1987, intended to supplement the existing 80 Class DMUs then in service.

[citation needed] In 2005, the entire fleet underwent an extensive refurbishment to bring them up to a similar standard to the newly introduced 3000 Class units, enabling them to remain in service for at least another 5 to 7 years.

During a two-day operation, the set was split into Driving Trailer, Intermediate and Power Car at Belfast and then, one-by-one, the carriages were taken by lorry to Downpatrick where they were reassembled.

The complete 458 successfully ran under its own power on 11 October 2014, and one week later on 18 October 2014, made a surprise appearance at the Irish Traction Group's Diesel Gala—the first time the unit had carried passengers since withdrawal by NIR in 2012.

In Autumn 2021, 458 was used in the filming of a season 3 episode of Derry Girls, with DCDR standing in for the Belfast–Derry and Coleraine–Portrush lines.