The NZR BB class of steam locomotives comprised 30 engines operated by the New Zealand Railways (NZR) in the North Island of New Zealand. Ordered to replace smaller locomotives of several classes in the North Island, they were similar in design and appearance to the preceding B and BA classes. The first BB class locomotive entered service in February 1915, with the last to commence operations doing so on 8 March 1917. All were built by A & G Price Ltd of Thames, New Zealand, and as their cylinders had a larger diameter than the B and BA locomotives they were capable of generating more power to haul heavier trains. The most visible difference however was the roundtop firebox in place of the preceding classes Belpaire design. The BB class could haul up to of freight on a level railway line, though they were limited to a top speed of around .
