They were designed primarily for use on freight trains in the South Island, and were capable of hauling a load of goods at speeds up to 30 mph (48 km/h).

The upgraded engines were capable of producing more power: their boiler pressure was raised to 200 psi (1,379 kPa) and they could generate 21,200 lbf (94 kN).

Like many classes of specialised freight engines on NZR, eight of the ten BA locomotives were modified to perform shunting duties.

With the arrival of more powerful mixed traffic engines in from the 1920s' onward, the BA class were largely confined to heavy shunting duties and short-haul freight services in and around Dunedin.

Some members of the class were transferred in the 1950s to the West Coast, where they operated for a few years on both shunting and longer distance services, notably on the line to Westport.