NZR UB class
UB class in the United States, prior to being delivered to New Zealand. The locomotive was renumbered no. 371 by NZR. A P Godber Collection, Alexander Turnbull Library
Type and origin Power type Steam Builder Baldwin Locomotive Works, Brooks Locomotive Works, Richmond Locomotive Works Build date 1898, 1901 Total produced 22
Specifications Configuration: ​  • Whyte 4-6-0 Gauge 3 ft 6 in (1,067 mm) Driver dia. 49.125 in (1.248 m) Adhesive weight 26.4 long tons (26.8 tonnes; 29.6 short tons) Total weight 57.8 long tons (58.7 tonnes; 64.7 short tons) Fuel type Coal Firebox: ​  • Grate area 16 sq ft (1.5 m2) Boiler pressure 175 lbf/in2 (1,207 kPa) (1898) 200 psi (1,379 kPa) (1901) Heating surface 1,324 sq ft (123.0 m2) Cylinders Two, outside Cylinder size 16 in × 20 in (406 mm × 508 mm)
Performance figures Tractive effort 14,590 lbf (64.90 kN) (1898) 16,670 lbf (74.15 kN) (1901)
Career Operators NZR Disposition Withdrawn

The NZR U^B class were a series of Ten Wheelers built by American manufacturers for New Zealand Railways (NZR) around the start of the twentieth century. Two batches were built by Baldwin in 1898 and 1901 (ten each).^[1] The earlier engines had slide valves and inside Stephenson motion, the later had piston valves and Walschaerts valve gear, as well as a higher boiler pressure.

Two additional locomotives were obtained in 1901 from ALCO, one each from Brooks and Richmond.

• The Brooks locomotive (#17) was heavier (30.1 long tons adhesive weight) with attendant increase in tractive effort (18340 lbf), and had a larger grate (17 sq ft). This locomotive was very popular with crews. This locomotive was dumped on the Oamaru foreshore.^{[citation needed]}
• The Richmond locomotive had less evaporative heating surface but included a superheater. Boiler pressure was lower (180 psi) and tractive effort was marginally lower.

The locomotives were initially assigned to Dunedin to Christchurch expresses and were reassigned as newer power replaced them. The last assignment for the class was on the West Coast Region.^[1]