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.

However, they arrived at the same time as the AB class Pacific, and as these proved equally adept at hauling freight trains of similar tonnage they were proliferated while no further BB types were ordered.

Accordingly, ten members of the BB class were modified to perform shunting duties between 1932 and 1938, and they successfully took on the heaviest of roles.

Today it is leased to Ian Welch and is under restoration at the Mainline Steam Heritage Trust's Parnell depot.