Alvis Stalwart The FV 620 Stalwart , informally known by servicemen as the ' Stolly ' , is a highly mobile amphibious military truck built by Alvis that served with the British Army . History . The Stalwart was a private venture by Alvis that was adopted and entered service with the British Army in 1966 as a general transport truck in preference to the FV431 , the load carrier variant of the FV430 series . It was one of the same line of vehicles that included the Alvis Saracen , Saladin and Salamander . The high mobility and amphibious capabilities were considered ideal for resupplying units in the field . Design . The hull is the vehicle chassis , the engine is situated under the load deck in the rear of the hull and the gearboxes , differentials and transfer boxes forward of this . The load deck was open - topped with large drop down panels on either side . Waterproof seals ensured that these would not leak when in the water . The three man cab has the driver ' s position in the centre and a seat for a passenger either side . The cab can only be entered through roof hatches . The Stalwart could carry 5 tonnes of stores , or tow 10 tonnes . In the water it was driven by vectored thrust water - jet propulsion units at about 6 knots . The drive system including the all - wheel drive , multiple gearboxes , and the water propulsion units was complex and needed a lot of maintenance . When the amphibious qualities become unnecessary , it was common for the water jets to be removed to reduce weight and maintenance . The Stalwart ' s impressive over - terrain capabilities came from the fact that the 6 - wheel - drive system lacked differential s , using simple bevel gears to transmit drive . A centre mounted no - spin differential allowed a certain amount of slip between the two sets of wheels on each side of the vehicle on hard surfaces , but there was no allowance for rotational speed differences between front and rear . The centre no - spin unit allowed the wheels on either side of the vehicle with most grip to drive when off - road . This had the effect of making the vehicle appear to crab ( move from side to side ) when negotiating muddy conditions , thus making the Stalwart a true 6 - wheel - drive vehicle , with 3 wheels locked together and turning at the same speed . However , this system caused ' wind up ' in the transmission ( inter - component stress ) as all the wheels were forced to rotate at the same speed , which during cornering is impossible . This led to rapid wear and breakage of the bevel gear boxes 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 enthusiast Stalwart owners – to get a vehicle to a show either requires moving it by low - loader or driving it on the road , risking damage to the transmission . Alternatively the front and rear driveshafts could be removed , eliminating windup at the expense of off - road capability . During military use the problem of transmission ' wind up ' was solved by laying out railway sleepers in a grid on flat ground and driving over them if on long road moves , this allowed the transmission to ' unwind ' . On more than one occasion , servicemen drove Stalwarts into car parks and used the kerbstones separating parking bays for the same purpose . . . quite unofficially . Another problem with the transmission was that the vehicle was designed to be driven ' loaded ' . Driving it ' unloaded ' caused increased wear on the drivelines to the wheels as a result of the increased angle of mesh of the joints . First model Stalwart Mk 1 Stalwart Mk 2 General Service . This had a 2 - man crew although a 3rd seat could be fitted to the right of the driver as a field modification . Could also carry 38 fully equipped troops or the Gloster SARO Bulk Refuelling Pack as alternatives to the 5 Ton cargo . The jet drive units in all the Mk 2 variants were much more efficient , giving a claimed 9 knots . Variants . The most obvious visible difference is that the lower edges of the cab windows were now angled downwards rather than horizontal . This was to improve visibility at close - range , particularly when being marshalled by a banksman standing nearby . Stalwart Mk 2 Limber . An artillery ammunition supply vehicle . Extra seat in cab for crane operator plus 4 extra seats , and an ATLAS 3001 / 66 hydraulic crane was added to the cargo area . REME fitter ' s vehicle , based on the Mk 2 Stalwart . Two extra seats were added and a different crane from the FV623 variant .