In 1918, NBL produced the first prototype of the Anglo-American Mark VIII battlefield tank for the Allied armies, but with the Armistice it did not go into production.

This included North America (Canada, Mexico, Newfoundland), South America (Argentina, Chile, Paraguay), Europe (France, Greece, Ireland, Italy, Netherlands, Spain, Turkey), Sub-Saharan Africa (Angola, Gold Coast (now Ghana), Kenya/Uganda/Tanzania, Malawi, Rhodesia (now Zimbabwe), South Africa); Middle East (Egypt, Palestine), Asia (India, Ceylon (now Sri Lanka), China, Japan, Malaysia, Philippines); and Australasia (Australia, New Zealand).

In 1935, NBL supplied six Palestine Railways P class 4-6-0 locomotives to haul main line trains between Haifa and the Suez Canal.

In 1949, South African Railways bought more than 100 2-8-4 locomotives from NBL and these became the Class 24; some operated tourist trains on the George-Knysna line until 2000.

As of January 2010, Umgeni Steam Railway operates SAR Class 3BR engine 1486, (NBL 19690 of 1912) and now named "Maureen", on the line between Kloof and Inchanga, a distance of about 23.5 kilometres (14.6 mi).

In 1922, the New Zealand Railways Department ordered a batch of its very successful AB class Pacifics from NBL, to be built and shipped as soon as possible.

22878 and 22879 were loaded aboard SS Wiltshire and she sailed for Auckland, New Zealand, but she got into difficulty at Rosalie Bay, on the east coast of Great Barrier Island and sank.

Due to the TFS headquarters being sold from under them, 22880 was put on the market, and has been taken into storage by Rimutaka Incline Railway Heritage Trust, after the Taranaki Flyer Society was liquidated in December 2013.

In the late 1950s, North British signed a deal with the German company MAN to construct further diesel engines under licence.

A partial reprieve came when money was made available to extend the electrification of the WCML north to Glasgow but no immediate funds were available for more electric locomotives.

In 1959, GEC, Clydesdale Bank and HM Treasury invested in a restructuring programme at North British to enable the transition of the company from steam to diesel-electric and electric locomotive manufacture, centred around production of the Class AL4.

Perhaps unwisely, North British supplied many of its diesel and electric locomotives to BR at a loss, hoping to make up for that on massive future orders that never came.

[citation needed] That, and the continuing stream of warranty claims to cure design and workmanship faults, proved fatal.