The locomotive was greatly improved from the
Class NG G11, with trailing wheels added to each engine unit, outside bar frames instead of plate frames, round-topped fireboxes instead of
Belpaire fireboxes, and larger dimensions in most respects except the grate area. They were superheated and sported an extremely compact arrangement of
Walschaerts valve gear and outside bar frames. The leading wheels were arranged as conventional
pony trucks, while the inner carrying wheels were built to the
Gölsdorf system which allowed the axle some lateral movement. Some rectifiable shortcomings were cylinders with old-fashioned short-travel valves with Z-ported cylinders, plain bearings on the inner carrying wheels that were inclined to run hot and a cab that was too small and unbearably hot in summer. The heat was made worse by the steam turret, vacuum-brake ejector and sight-feed lubricator that were placed inside the cab. Since the seats of the driver and stoker were mounted on poles which allowed them to be swung around to outside the cab, crews could often be seen riding outside to escape the heat. As built, the sandboxes were mounted on the front of the water tank and rear of the coal bunker, one on either side of each headlight. On some locomotives the front sandboxes were later relocated to the top of the tank. ==Service==