The Baldwin Locomotive Works in the United States supplied the first two 2-6-2tank locomotives, as well as a range of spare parts. These were used to construct locomotives 3 and 4, with further examples of the class entering service up to the last, number 17, in 1915. Engines 2 and 4 used compound high- and low-pressure cylinders, while the rest of the class used simple expansion.
By the mid-1920s these small locomotives were not able to handle the increasing traffic, and two G classGarratt locomotives were purchased to supplement the fleet.
The locomotives weigh 36.58 long tons (37.17 t; 40.97 short tons) and produce a tractive effort of 12,170 lbf (54.1 kN), allowing them to haul loads of 90 long tons (91 t; 100 short tons) up grades of 1 in 30 (3.33%). Numbers 6, 7, 8, 12, and 14 have been restored and operate on the Puffing Billy Railway, and No. 3 is also on the Puffing Billy Railway, awaiting eventual restoration. The remaining locomotives have all been scrapped.
A 101⁄4 in (260 mm) gauge replica of a NA class locomotive was built in 1993 for use on the Isle of Mull Railway. The engine, named "Victoria", was built by the Mouse Boiler Works, using drawings provided by the Puffing Billy Railway. It operated on the Isle of Mull until the railway's closure in 2011, and is currently operating on the Rudyard Lake Steam Railway.