Image: A 1962 factory photo of an M.R.S. model I-90 tractor unit with normal factory accessories (including the dozer blade). This is a Cummins C-160 CI-powered example. These tractor units could have manual or powershift transmissions depending on the customer’s requirements.
Richard Campbell reviews a US manufacturer of four-wheel drive towing vehicles used by all branches of the United States armed services and found to be highly versatile and rugged for civil contracting operations.
The Mississippi Road Supply Company (M.R.S.) was founded in 1943 in Jackson, Mississippi and, following WW2, a shift was made to larger premises in Flora, Mississippi, on the site of an ex-US Army ammunition manufacturing & storage depot.
During the war years, most of the attachments for these machines were supplied to M.R.S. by Bucyrus-Erie.
Following WW2, many of these machines were sold off as army surplus and found their way into civilian hands, where they were used in construction and agriculture.
They proved to be very versatile and were well-accepted in civilian use.
The popularity of their machines in ‘non-combat’ service was not lost on the company, and M.R.S. began to develop further different types of tractor units to suit this new market.
As Bucyrus-Erie had now become a prime supplier of bulldozer blades, scrapers, and other equipment to International Harvester, the supply of this ancillary equipment could not be guaranteed, so M.R.S. sought alternative supply sources and, before long, formed an alliance with the Wooldridge Manufacturing Company of Sunnyvale, California.
This arrangement, which was beneficial to both parties, lasted from 1946 until 1958 and was responsible for the development of some of the largest single open bowl scrapers ever built.
The tractors
M.R.S. tractors were primarily ‘assembled’ machines. By this, I mean that while M.R.S. built the chassis and some primary systems, all the other necessary components (engine, transmission, differentials, pumps, final drives, etc.) were supplied by outside manufacturers, similar to the way that Peterbilt or Kenworth build trucks.
Customers would specify their choice of powerplant, transmission, etc., and M.R.S, would set up and manufacture the tractor unit to the customer’s specification.
Then Wooldridge would manufacture and supply any additional products that the customer wanted to be fitted to complete the order – scraper, dozer blade and cable controls – and job done.
So, an M.R.S. tractor could be powered by a GM, Cummins, Buda or Caterpillar (rare) diesel engine, Allison, Spicer or Fuller gearbox, Clark axles etc.
While this arrangement suited the customer, it made parts sourcing for a traded-in machine a nightmare.
M.R.S. only ever manufactured four-wheel prime movers, and one of its unique features was its four-wheel drive and steering systems, which allowed the machines to traverse all manner of hostile landscapes without becoming bogged.
Even ‘crab steering’ was possible, if necessary, to get around obstacles.
Their all-wheel drive nature also gave the machines tremendous useable traction for self-loading. Other features incorporated into M.R.S. tractor units as standard included a front push plate or blade, and a traction aid control on some of the larger model tractor units that transferred weight, via a large single-acting hydraulic cylinder, from the scraper to the tractor’s rear drive axle.
Who’s buying?
As mentioned previously, M.R.S.’s primary customer was the United States military.
Although M.R.S. also manufactured for the domestic US construction market, this seems to have been fairly localized as the big money always remained with government contracts.
There was also quite a bit of competition in this market, primarily from Clark Equipment, FWD-Wagner and old favourites Caterpillar; companies who all developed machines to vie for a slice of the government pie.
In almost all cases, regardless of supplier, the machines offered had an ‘M’ in their designation standing for Military.
Supply problems
In 1958, M.R.S.’s principal supplier of ancillary equipment, Wooldridge, were bought out by the Curtiss-Wright Corporation and M.R.S. was suddenly left without an equipment supplier. A hasty deal was struck with Euclid Road Machinery to maintain supply of scraper bowls and around the same time, M.R.S. also concluded a deal with Hancock to supply the new elevating scraper bowls which were just becoming available.
As a result of the equipment supply problems/uncertainties, M.R.S. decided that it would be a good idea to design and build their own, thus ensuring supply.
This turned out to be a very successful move, as from around 1967 onwards, the majority of M.R.S. machines were sold with their own equipment, M.R.S. eventually even producing their own elevating scraper units.
Common M.R.S. tractor units
The following list highlights the most commonly produced models and their types:
Open bowl: Model I-25 (8 cubic yards); I-95 (18 cubic yards); I-105 (24 cubic yards); I-110 (32 cubic yards); 200 (35 cubic yards) 250 (48+ cubic yards).
Elevating scrapers: I-80 (12 cubic yards); I-90 (14 cubic yards) I-100ES (18 cubic yards); I-110ES (32 cubic yards).
These tractor units were powered by a variety of engine/transmission combinations including International, Cummins & General Motors diesels with Allison, Spicer, Twin-Disc or Fuller gearboxes.
In service
In military service, M.R.S. machines were used worldwide, and especially so in Vietnam, where they saw extensive service.
As is the case when the military is finished with an item, many subsequently found their way into civilian hands via government disposal auctions, changing hands for sometimes less than their scrap value!
Epilogue and irony
The very nature of the way the M.R.S. machines were manufactured, and their limited production runs, meant that the machines became basically uneconomical to produce, and the company went out of business in the early 1980s.
Taylor Machine Works purchased all the assets of M.R.S. in the mid-1980s and continued to produce a small number of machines for outstanding customer orders. The M.R.S. brand is no longer offered today.
However, their simplicity and extremely rugged design and the very ‘kitset’ nature of the machines guaranteed them a long life, as components are still readily available from all those folks that originally supplied M.R.S.!
An M.R.S. model I-110 tractor unit even made its way to New Zealand in the 1970s, imported by Lion Machinery of Rotorua. This was converted into a self-propelled compactor and operated by Barry Andrews Earthmovers on the police training college site at Porirua in 1975.
It was last seen rusting away on a used machinery lot in Rotorua, gutted of its GM 12V-71 engine.
For the model collector
Surprisingly, considering the rather low profile of M.R.S., there is a limited-edition model available of one of their machines – a Model I-250 tractor unit with Wooldridge OS-400 cable-controlled scraper.
This is to 1:50th scale and produced by EMD Models – worth adding to your collection, if you can find one.
Handing over the baton