The prototype locomotive had an interesting history. In 1928 the New Zealand Government Railways imported three Beyer Garret 4-6-2 + 2-6-4 locomotives which, for a variety of reasons were not a success. In 1937 the three 'G' class locomotives were dismantled and the engine chassis were used to build the six Pacific class locomotives which retained the classification of 'G'. They were popularly known as 'half Gs' in some quarters. Local readers will recognise the derivation of that name from the popular name for half gallon flagons of draught beer which were almost part of the New Zealand staple diet at one time.

In their new guise the locomotives were more successful, but still not really up to scratch. They required a great deal of maintenance. Main frames were prone to cracking from excessive flexing and the valve gear was generally thought to be too light for the job being done. An interesting feature of these locomotives was the outside conjugated valve gear for the third cylinder. The levers for this gear were driven from the spindles of the valves of the two outside cylinders with the motion being timed through asymmetrical levers across the front of the locomotive. They were fascinating to watch on the prototype and I find them just as cute on the model when it is running.