This is the lunatic six-wheel Mercedes G63 AMG 6x6, the largest and most extreme road legal SUV to ever hail from Mercedes' road car operations.

Produced on a limited basis – and at a price of £370,000 – the colossal double-cab pickup started life as an even more rugged military version of the G320 CDI conceived and engineered for the Australian army and in operation since 2011.

This plush, leather-lined civilian version of the off-road vehicle has been conceived to appeal to some of Mercedes-Benz's most affluent clientele.

It features six driven wheels, low range gearing, five differential locks and a tyre control system for its standard 37-inch wheels. Mercedes says it is "the last word in forward-thrusting power for the beaten track".

Unlike the military version of the G320 CDI 6x6, which is fitted with Mercedes-Benz's 3.0-litre V6 diesel and is offered in outputs of up to 220bhp, the G63 AMG 6x6 gets a twin-turbocharged 5.5-litre V8 from AMG with 536bhp. Torque is a 560lb ft – crucial in providing the shove required to haul the big four-seater’s considerable 3775kg kerb weight.

Mercedes' 7G-tronic seven-speed automatic transmission is fitted in place of the old NAG1 five-speed auto 'box found on the army version. Its transfer case can alter between a 0.87:1 high-range ratio for on-road driving and 2.16:1 low-range ratio for off-road conditions to all six wheels in a nominal 30:40:30 split. Power for the rearmost axle is supplied by an extra shaft. There are five electronic differential locks offering 100 per cent lock up of all six wheels, operated by three switches on the dashboard.

Relaying the engine's strong reserves to the ground are massive 37-inch wheels featuring a bead-plate design. They are shod with 12.5in-wide wheels. 

At 5875mm in length, 2110mm in width and 2210mm in height, the G63 AMG 6x6 is 1106mm longer, 225mm wider and 272mm higher than the G63 AMG. Along with a 300mm increase in the wheelbase through to the middle axle at 3120mm, the front and middle axles have increased in width by 281mm each at 1790mm, requiring widened and lengthened carbonfibre guards to cover the huge wheels.

Ground clearance is a whopping 460mm while fording depth is put at 1000mm – some 250mm and 400mm more than the standard car. Approach and departure angles have been increased by 16 degrees and 27 degrees at 52 degrees and 54 degrees respectively, while the breakover angle has increased by 1 degree at 22 degrees.

To drive, it's a blast, at least in the wide-open space of a Dubai desert where the G63 AMG 6x6 has sufficient room to strut its stuff. I'm not sure how it would fare during the morning rush hour, but there’s no doubt you'd be noticed. And really, that's what this new Mercedes-Benz is all about. 

That said, the example we drove was terrifically engineered – as complete from a technical standpoint as you'd expect any model from the German car maker whose first 6x6 customer deliveries are planned to get underway in just six months' time. 

Before we got behind the wheel, we were taken for a wild ride over the dunes by a Mercedes test driver, who performed a round of donuts to prove how well engineered the G63 AMG 6x6 really is. The fact that it was originally conceived for military use helps, of course. The big surprise is just how refined it is. 

Once you’ve heaved yourself on to the substantial step plate and introduced your backside to the leather-lined comfort of the G63 AMG 6x6's heavily contoured sport seat, you discover a cabin changed little from the standard G63 AMG up front.

The upright driving position is old school, as is the steeply angled windscreen and shallow dashboard. But forward vision is brilliant and indicators mounted on the front fenders act as positioning points. Rear vision is hampered by the tall rear seatbacks and a small two-piece sliding rear window.

At 3120mm, there's a 300mm increase in wheelbase to the first of the rear axles. It provides a longer cabin than the standard G63 AMG – and with it additional rear legroom. There's a liberal covering of Alcantara throughout and the standard three-across rear bench seat is replaced by two individual AMG sport seats. They get electronic backrest adjustment and are divided by a rear centre console.

There's an engaging blare through the four sidepipes as you hit the starter button to fire the engine, lending the big Mercedes an eager demeanour. Blip the throttle and it squats on its springs under load change like a true muscle car.

Once underway, the G63 AMG 6x6 proves remarkably easy to drive. It may have been conceived for the rough-and-tumble of army duties in the Australian outback, but the work put in to converting it for civilian use has produced a straightforward nature together with level of comfort you'd hardly credit from such an extreme-looking machine. 

In the dunes of the Dubai desert, the G63 AMG 6x6 feels invincible. Those big tyres work with the complex driveline to provide plenty of traction, allowing you to wind it up to regular motorway speeds on narrow sandy tracks without any great trepidation. 

It cruises with great authority, providing longitudinal stability – far better than the regular G63 AMG owing to the longer wheelbase and added traction provided by the third axle. There's far less vertical movement through the suspension than the standard car, resulting in a surprisingly smooth ride. There's plenty of lean in corners, but body movements are controlled thanks to a unique spring and damper package developed specifically for the G63 AMG 6x6.

Despite its weight, it accelerates with great vigour. Heady torque combines with the traction-enhancing qualities brought by the six-wheel-drive system to deliver impressive off-the-line and in-gear qualities. Mercedes won't quote official acceleration claims just yet, but insiders suggest 0-62mph in less than six seconds. Top speed, limited by its balloon-like tyres, will likely be electronically governed to 100mph.

And consumption? Again, Mercedes is yet to publish official figures, but we're told to expect around 15mpg on the European test cycle. It's just as well that the G63 AMG 6x6 will come with two fuel tanks with an overall capacity of 159 litres.

The prototype's vague, hydraulically-operated steering, which is geared at a lazy 3.4 turns lock-to-lock, indicates the need for some fine-tuning to better suit the big tyres. But any doubts about dynamic ability on the back of its rugged good looks were quickly dispelled. 

Even when confronted with steep dunes and daunting sink holes, the hulking SUV managed to take it all in its stride, powering on with determination and a baritone exhaust note. Excellent wheel articulation and myriad diff lock combinations keep all six wheels firmly planted on the ground for impressive progress. An onboard compressor with four 20-litre tanks fitted along the sides of the underbody allow you to adjust tyre pressures, taking just 20sec to increase from a stand-friendly 0.5bar up to the 1.8bar required for on-road use – much faster than a conventional system that typically takes around 10mins.

The only thing I've driven that comes remotely close to the feeling I got while at the wheel of the G63 AMG 6x6 is the Hummer H1. But while the former is incredibly nimble for something so vast and hugely powerful, the latter was stodgy and rather lethargic. 

You could argue long and hard about the merits or otherwise of the G63 AMG 6x6 – surely the world's first road legal MUV (monster utility vehicle). However, one thing holds true: it is a fun thing to drive in the right conditions.

But with a price tag more than three times that of the G63 AMG, it is going to be a super-exclusive proposition for all but the mega-rich.

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