| Driving Wheels | 4ft 6ins |
| Weight | 85 tons |
| Boiler Pressure | 180psi |
| Cylinders | Outside – 17in x 26in |
| Tractive Effort | 20,030 lbf |
A total of 141 class AB locomotives were built for the New Zealand Railways (NZR).
In 1906 the NZR built an experimental 4-6-2 locomotive at Addington Railway Workshops.
In 1915 the first of the class AB was built by the NZR which incorporated a number of improvements to the earlier locomotive. Of the 141 locomotives 38 were built at the Addington Railway Workshops, 20 by A & G Price in Australia and 83 by the North British Locomotive Company in Glasgow.
The locomotives were efficient and versatile and were easy to maintain and operate. However, it became clear that there were several shortcomings of the design – notably the cab was too small, and the tenders were not sturdy enough. As a result a longer cab was fitted to all new locomotives built after about 50 had been completed. New tender structures were also built at a later date.
Being highly capable, the AB class were used for both freight and passenger trains. They were easily able to pull an express passenger train at speeds of 62 mph, or haul 700-tonne goods trains on easy grades.
The locomotives did not change greatly during their NZR career. The first change was to fit Waikato-type spark arrestors to many of the North Island-based engines, resulting in a new ‘pear-shaped’ smokebox with an ash hopper at the base of the smokebox. The cast-iron smokebox doors were replaced by steel ones, and the brake pump was moved from its original location on the right-hand side of the smokebox to a new position, recessed into the running board, just forward of the cab on the same side.
The AB class were used on almost every section of the NZR network apart from the Nelson Section which was closed in 1955. In later years, the class were displaced from their mainline duties first by the larger J and K series locomotives, and later by the arrival of diesel locomotives. After the introduction of diesel locomotives in the North Island from 1955 onwards the class Ab locomotives there were moved to see out the rest of their working lives on the South Island.
The final duties of the locomotives were on branch line workings, where they found their niche after being displaced from most mainline duties by larger locomotives. The locomotives also worked some lesser mainline duties, and others, such as those at Gisborne, were used as bankers to assist trains heading south to Napier.
This locomotive was built by the North British Locomotive Company in Glasgow in 1922 and entered service on the NZR as AB 745.
In July 1956 the locomotive came to grief after heavy rain weakened an embankment just north of the station at Hawera. The locomotive was buried where it had fallen and the line reinstated on top of it.
In 2001 the engine was salvaged but the tender was left as it was considered to be too difficult to recover it and it was in a very poor condition. The Taranaki Flyer Society then started the long task of restoring the locomotive in an old goods shed at Stratford. By the time the locomotive was moved from Stratford to Maymorn in October 2013 the boiler had been lifted from the frames, the frames and wheels had been cleaned down and parts carefully stripped down and stored. Many of the parts found to be missing or damaged beyond repair.
The Taranaki Flyer Society subsequently signed an agreement giving the Rimutaka Incline Railway ownership of the locomotive and it moved to the railway at Maymorn in the Wellington region of New Zealand in 2013. The restoration work is continuing at the Rimutaka Incline Railway.
One other AB class locomotive built by the North British Locomotive Company has been preserved.
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