The Stalwart, formally classified by the British Army as Truck, High Mobility Load Carrier (HMLC), 5 Ton, 6 x 6, Alvis Stalwart and informally known by servicemen as the Stolly, and by former RCT as the Stally, is a highly mobile amphibious military truck. Built by Alvis Cars between 1960 and 1971, these vehicles served with the British Army from 1963 until 1993.
History
Alvis had great success with the FV603 Saracen armoured personnel carrier, being produced from 1952. The Saracen had permanent 6 wheel drive, and independent parallel wishbone links and torsion bar suspension on each wheel station. Alvis then used the same suspension and drive methods to develop the FV601 Saladin armoured car, and the Salamander airfield crash tender. Following the success of those vehicles, Alvis then decided to start a private venture of an off-road truck, capable of carrying 5 tons and being highly mobile. Using the hull and cab of the Salamander, Alvis created the 'Camion' for the military and civilian market. The military, having conducted fording trials with the Saracen, asked if Camion would float. Camion is commonly known by its chassis number of PV 1 (Project Vehicle 1), and as "The Beast" by staff at Alvis. While the military carried out fording trials at Instow, Alvis went away and developed PV 2. PV 2 was put through a number of trials and tests both in the UK and Sweden, and received various facelifts to the cab roof and body sides along the way. The final version of PV 2 has twin hatches and a Hiab crane, compared to the original having full-length sideboards and a sliding roof hatch. PV 2 was named Stalwart. The Stalwart was adopted and entered service with the British Army in 1964 as a general transport truck in preference to the FV431, the load carrier variant of the FV430 series. The high mobility and amphibious capabilities were considered ideal for resupplying units in the field, particularly those of the British Army of the Rhine.
Design
The Stalwart is a frameless vehicle with an all welded waterproof hull - the hull forms a punt chassis. The engine is situated under the load deck in the rear of the hull and the gearbox with transfer box and differential forward of this. The load deck is open-topped with large drop-down panels on either side and rear. Waterproof seals ensure that these will not leak when in the water. The cab has the driver's position in the centre, and a seat for a passenger on the left side of the cab or either side on some models. The cab can only be entered through roof hatches. The dropping side windows are emergency escape hatches.
The Stalwart can carry 5 tonnes of stores. Early press releases in Commercial Motor suggests it could tow 10 tonnes. But trial reports by MEXE showed it could easily handle 7.5 ton.
In the water it can be driven at about 6 knots by vectored thrust water-jet propulsion units.
The drive system, which includes the all-wheel drive, multiple gearboxes, and the water propulsion units, is complex and needed a lot of maintenance. When the amphibious qualities became unnecessary, it was common for the water jets to be removed to reduce weight and maintenance.
The Stalwart's over-terrain capabilities come from the fact that the six-wheel-drive system lacks differentials, using simple bevel gears to transmit drive. A centre-mounted no-spin differential allows a certain amount of slip between the two sets of wheels on each side of the vehicle on hard surfaces, but there is no allowance for rotational speed differences between front and rear. The centre no-spin unit allows the wheels on either side of the vehicle with most grip to drive when off-road. This has the effect of making the vehicle appear to crab (move from side to side) when negotiating muddy conditions, thus making the Stalwart a true six-wheel-drive vehicle, with three wheels locked together and turning at the same speed.
However, this system causes "wind up" in the transmission (inter-component stress) as all the wheels are forced to rotate at the same speed, which during cornering is impossible. This led to rapid wear and breakage of the tracta joints within the drive train if the vehicle was used on firm surfaces, such as tarmac or concrete; in off-road conditions, the natural 'slip' of a loose surface, such as mud or gravel, reduced wind up. This problem is of special concern for modern-day Stalwart owners – to get a vehicle to a show requires moving it by low-loader or driving it on the road, risking damage to the transmission. Alternatively, the front and rear driveshafts can be removed, eliminating wind-up at the expense of off-road capability.