Introduced from 1939, the N type carriages were a further development of the earlier all-steel S type cars, built by Clyde Engineering to bolster the NSW Government Railways’ locomotive-hauled fleet. A total of 212 vehicles were constructed between 1939 and 1949, divided into FN second-class cars and BN first-class cars.

The N type carriages were delivered in dedicated "sets" - referred to as NUB sets. Each set comprised of seven cars - five second class cars and two first class cars.

Compared with their predecessors the S type carriages, the N types were slightly longer, riding on a 62-foot (18.9-metre) underframe rather than the S type’s 59-foot base. They offered larger compartments and a smoother ride, aided by improved bogies. They were corridor compartment stock with riveted steel bodies, vestibules at each end, and lavatories off the vestibules.

A BN first-class carriage seated 42 passengers in seven roomy compartments, while an FN second-class carriage seated 64 across eight compartments. Their appearance was near-identical to the S cars, making them easily interchangeable in service, but they were regarded as a refinement - more comfortable and modern in finish.