The NZR RM class Clayton steam rail motor was a unique railcar that was operated by New Zealand Railways (NZR) for New Zealand's national rail network and one of only two steam railcars to operate in New Zealand - the other being 1925's RM class Sentinel-Cammell.

The RM class was the classification used by the New Zealand Railways Department (NZR) and its successors gave to most railcars and railbuses that have operated on New Zealand's national rail network. "RM" stands for Rail Motor which was the common name at the turn of the 20th century for what became known in New Zealand as railcars. As many types of railcars are operated, class names have been given to each railcar type to differentiate them from others.