NZR RM class (Wairarapa)

NZR RM class Wairarapa
The sole surviving Wairarapa railcar, RM 5 (Mahuhu), undergoing restoration at the Pahiatua Railcar Society.
In service	1936–1955
Manufacturer	New Zealand Government Railways
Built at	Hutt Workshops
Entered service	September–December 1936 (RM 4–9); March 1937 (RM 10).
Number built	7
Number in service	None
Number preserved	1
Fleet numbers	RM 4–RM 10
Capacity	RM 4–9: 49 passengers. RM 10: 20 passengers, 3 tons freight.
Operator(s)	New Zealand Government Railways
Line(s) served	Rimutaka Incline; Wairarapa Line
Specifications
Car length	57 ft 11 in (17.65 m) over buffers
Maximum speed	60 mph (97 km/h)
Weight	13.56 tonnes (13.35 long tons; 14.95 short tons)
Prime mover(s)	Originally six-cylinder 10-litre Leyland petrol engine. From 1940–41, six-cylinder 10-litre Leyland Diesel engine
Power output	130 hp (97 kW) (petrol) 119 hp (89 kW) (diesel)
Transmission	Mechanical
UIC classification	2-A
Bogies	One bogie (front, unpowered), one single axle (rear, powered).
Multiple working	No
Track gauge	3 ft 6 in (1,067 mm)

The NZR RM class Wairarapa railcar (or Rimutaka railcar) was the second truly successful class of railcars to enter service on New Zealand's national rail network. They entered service in 1936 (three weeks after the Midland railcars) and were classified RM like all other classes of railcars in New Zealand; they came to be known as the "Wairarapa" class (and sometimes as the "Rimutaka" class) as they were designed to operate over the famous Rimutaka Incline to the Wairarapa region on the Wairarapa Line. They also acquired the nickname of "tin hares" in New Zealand railfan jargon. The first two to be introduced re-used the numbers RM 4 and RM 5 that had previously been used by the withdrawn experimental Model T Ford railcars. The class consisted of six passenger railcars, and one passenger-freight railcar. It is often described incorrectly as a class of six railcars.

The Rimutaka Incline over the Rimutaka Ranges posed a severe time delay to any service operating between Wellington and the Wairarapa region. At one end of the Incline, a train had to have its engine replaced by multiple members of the H class, as the H class locomotives were specially designed to work the steep and difficult Incline. Once they hauled the train the length of the Incline, they were then replaced by a single ordinary engine. The procedure to attach and remove the H class locomotives, as well as the actual trip along the Incline, was very slow.

The Wairarapa railcars were designed as an answer to this problem. They were intended to operate along the length of the Incline and take over Wairarapa passenger services from regular carriage trains. Their body was built higher than an ordinary railcar, with a raised floor, to enable them to pass over the raised Fell centre rail on the Rimutaka Incline. In design, they resembled a bus, and unlike a usual single-unit railcar that has a driving compartment at each end, the Wairarapa railcars only had one driving end, necessitating that they be turned at the terminus of their journey.