Contractor Tank Transporter
Although only rated as a 61-Tonner, the military Contractor was broadly based on its civilian counterpart, rated at 240-Tons. The most significant changes are the addition of special equipment for military purposes and the lack of options available to civilian users.
Civilian users had the choice of engines from Cummins, Rolls Royce, Leyland and AEC which ranged from 240 to 400 bhp. The military spec used the Cummins NT335 turbo-charged, 6-cylinder rated at 335 bhp. Turbo-charging was regarded as essential for operation at high altitudes and allowed no loss of power up to 3600 metres above sea level. This was the only engine option offered.
Whereas civilian operators could opt for the Self Changing Gears RV30 semi-auto gearbox, the military version was only available with the Fuller 15-speed, twin countershaft gearbox. This provided 10 normal and 5 deep reduction gears.
In standard form the gearing provided a top speed of 59kph and the ability to climb a 1 in 5.1 gradient. Alternative ratios were obtainable by a simple workshop change, enabling a top speed of 73kph while being able to climb a 1 in 6.4 gradient. Enough fuel could be carried to provide a 300 mile range.
The engine and gearbox were coupled with a Lipe Rollway 15 inch, twin plate, air operated clutch.
The drive axles were the familiar Contractor bogie, with spiral bevel drive units and epicyclic reduction hubs. A third lockable differential ensured maximum traction, whatever the conditions. This bogie had been well proven with the Constructor before the Contractor and the Scammell range of desert and dump trucks.
Scammell's long experience in the Middle Eastern oilfields provided a cooling system capable of coping with temperatures of 52C (125F). To achieve this, a large frontal area radiator was used. The cast top and bottom tanks were detachable to facilitate easy maintenance and cleaning.
Standard Contractor hydraulic powered steering was used with a 8,130kg capacity front axle, equipped with shock absorbers and non-lubrication springs.
While operational tanks can easily and quickly be driven onto their transporters, the role of the transporter is also to recover stricken tanks. The Contractor was equipped with a vertically mounted drum winch mounted behind the cab. The large diameter drum helped reduce the bending stress on the 122 metres of 25mm rope, increasing rope life. A 'paying-in' guide ensured even layering of the rope.
The winch could only be operated with the winch brake cut-out employed. This prevented run back should the engine stall. A cut-out protected the winch or rope from overloading.
A dog clutch disengaged the winch drum for 'paying-out', allowing speedy deployment of the rope.
Lightweight single and double sheath pulleys with quick release pins for emergencies were fitted with anti-friction bearings with dust seals. Use of these pulleys allowed for a 50800kg line pull for recovery operations, including the facility to winch through the front of the Contractor for self-recovery.
The standard cab had seating for 2 crew with additional crew accommodation available as a canvas covered seating area fitted behind the cab above the winch. For hot climates a heat shield was fitted to the roof and air conditioning was available.
Further optional extras included roof mounted searchlights, ballast box instead of fifth-wheel and choice of rope length for the winch.
The trailer coupled to the unit by way of a fully oscillating fifth-wheel. This articulated about both its fore and aft axis and sideways axis to maximise stability on uneven ground. Bump stops were fitted to the fabricated saddle assembly to prevent damage during severe articulation on uneven ground. The trailer coupled to the fifth-wheel with an 89mm kingpin.
The 60,960kg capacity trailer was designed and built by Crane of Dereham and is possibly the last entirely Crane trailer designed before the company was absorbed into the Freuhauf group. The Crane running gear had been developed over many years experience with the Iraq Petroleum Company. Although a Crane design, the trailers carried the famous 'CF' badges.
Standard equipment included chain tensioners and track guides designed to adjust and suit varying types of tracks. These guides were removable to provide a flat bed allowing more general cargo such as stores or machinery to be carried. Loading was via fold down ramps which were adjustable for width to accommodate size of tank.
Hinged support legs capable of supporting a fully freighted trailer were mounted on the front corners of the bed, allowing the tractor unit to be used for other trailers if necessary.
The useable length of the trailer bed was 6.25 metres and the width, 3.65 metres.
The British Army favoured the 6x4 Crusader over the Contractor, leaving Scammell to look overseas for sales.
The Australian Army bought them, probably supplied in CKD form to Scammell's dealer facilities which was Scammell's normal practice for Australia. The Contractor had already gained an enviable reputation in the Australian mining industry.
The main market for the Contractor was the Middle East countries, where Scammell had long experience and first class reputation with oilfield and desert lorries.
Middle East countries using the Contractor included Kuwait and Iraq. The Jordanian army used the Contractor to supplement and replace their ageing Constructors, although these were used with Dyson 30-Ton multi-purpose trailers to carry 2 11-tonne M113's.
Kenya, Libya and Israel were users of the Contractor. The Israeli ones wore Leyland badges due to the political climate in the Middle East. Middle East countries would not deal with companies that supported Israel, so in preference to antagonising most of their Middle East customers, the Scammells became Leylands.
From my original article in Classic Military Vehicle, No. 56, January 2006.