Weighing 39.5 long tons (40.1 t; 44.2 short tons) with a tender of 27.4 long tons (27.8 t; 30.7 short tons), they could haul express trains easily at 50 miles per hour (80 km/h) on mainline railways that were flat or had only a light grade. It had 58 inches (1,473 mm) coupled driving wheels, which were large for the period, a working steam pressure of 185 pounds per square inch (1,276 kPa), and 16.5 inches (419 mm) diameter cylinders with 22 inches (559 mm) piston strokes. The handsome UD locomotives were more than capable of making up lost time, with mile-a-minute runs recalled with pride by Manawatu railway employees.
Although they were fast and powerful, the UD locomotives were unable to survive a programme of standardisation undertaken between 1925 and 1935 to eliminate small locomotive classes that were costly to maintain in favour of large, homogeneous types that provided economies of scale. They were written off in 1929.