Thirty-eight motor cars and thirty-one trailers were built between 1937 and 1954, split between six subtypes designated a through f. Class 91 was a further delivery of ten units that had a more comfortable interior and designed for regional trains.

The trains had good acceleration and a maximum speed of 100 kilometres per hour (62 mph), which made them suitable for most unelectrified lines in Norway.

The oldest units were originally equipped with MAN and DWK prime movers.

From the 1960s, all trains not retired received two Rolls-Royce C6SFLH engines with a power output of 158 kilowatts (212 hp) each.

Thirteen motor units and nine trailers have been preserved by various heritage railways and museums in Norway and Denmark.

The oldest units were equipped with Maschinenfabrik Augsburg-Nürnberg (MAN) and DWK prime movers.

[1] Later editions were originally equipped with two Hercules DFXH-F prime movers, each with a power output of 140 kilowatts (190 hp).

[2] Class 86 is based on a delivery of ten aluminum carriages by Strømmen to NSB in 1936 and 1938.

Starting in 1962, NSB began replacing the prime movers with Rolls-Royce C6SFLH; this was done on the e-series, the f-series and no.

Other renovations and upgrades were made, resulting in new series; by the class' retirement, the designation had reached m.[1] The class featured good acceleration and high top speed, making it suitable for and use on nearly all of NSB's unelectrified lines.

[6] Two Class 91 units have been preserved by the Norwegian Railway Club, one on the Krøderen Line and one at Marienborg.