Despite the good reputation enjoyed by Holmes, and the success of most of his designs, these locomotives are generally judged to have been a failure.

The original engine, number 592, was exhibited in Edinburgh before entering service, and had the unusual distinction of running through the city's public streets (under its own power) on temporary tracks when it was transferred back to the main line.

The single rebuilt locomotive was considered a different class (after rebuilding) by both companies, and was therefore designated L (NBR) or D36 (LNER).

The Class N (D25) engines were built for express passenger service when the NBR was preparing for significant expansion of its timetable following the reopening of the Tay Rail Bridge.

The engines performed admirably, and were popular with railway staff, several being recorded in use on Royal trains of the period.

[6] The class N (D35) engines were specially designed and built to operate the then brand new West Highland Line.

The engines were withdrawn prematurely between 1920 and 1924, having served well under 30 years, much of that time on shunting duties, with the single exception of the locomotive rebuilt as a class L (see below).

It was an attempt by William P. Reid to solve the problems of poor and inefficient running in the class N (D35) engines.

However, it remained less efficient than newer locomotive designs of a similar type, and the extent of the rebuild made it costly.