Originally built as a Petrol Electric Rail Motor (PERM), they were the longest-lived railmotor on the Victorian Railways, with the first entering service in 1928 and the last being withdrawn in 1991. The first railmotor was built by the Victorian railway Newport workshops not the built by the St. Louis Car Company It was powered by a 220 hp Winton petrol engine which was used until the 1950s when they were converted to twin Diesel Electric engines giving a total of 255 bhp.
By the 1970s the longest regular scheduled journey run by a DERM was the Bendigo to Robinvale run, withdrawn on 3 June 1978. A DERM with a DERM Trailer car ran a regular passenger train on the South Gippsland Line from the 1960s - 1970s. In the late '70s RM 55 and RM 61 were extensively modified with the cab being rebuilt, the engine being relocated and the engine room rebuilt with porthole windows, and new aluminium cabin windows fitted. As such they looked significantly different.
DERMs with the porthole windows were a familiar sight on the Mornington and Stony Point lines prior to the line closures in the early 1980s.
As of 1983, 28MT had been scrapped and 27, 29 and 30MT were all withdrawn account poor condition, and the Brill trailer 200MT was stored unservicable at Newport workshops. 26MT was still in use along with the ex-W-type trailers 31MT, 32MT, 33MT and 34MT.
All but one of the DERMs have survived into preservation, with 57RM being the only DERM to have been scrapped. Four are operational, with the remaining five in various conditions. Below is a brief outline of the status of the DERMs (as at February 2016):