Designed to be able to operate non-stop for distances of up to 100 miles (161km), the first of the 36-class entered service in 1925. Nos 1 to 10 were built by the NSW Government Railways at Eveleigh (Redfern, Sydney), while the remaining 65 were constructed by Clyde Engineering. 

An interesting quirk saw the Clyde-built locomotives finished before the NSWGR built engines, which meant that 3610 was the last of the class to enter service. 

The 36 class locomotives were originally fitted with round-top boilers, which gave them a somewhat porcine appearance, and this, coupled with difficulties in firing their narrow fireboxes and the regular repairs required to the boilers, led to the nickname ‘Pig’. Most of them were re-boilered with Belpaire fireboxes and given new style cabs to match during their service lives, although the nickname remained.

With the 36 class came the introduction to the NSW railways of the ‘turret’ style tenders, which gave the crews better vision when travelling in reverse.

Locomotive 3642 entered traffic in January 1926 and was withdrawn from active service in November 1969 before being retained for the NSW Rail Museum.