IT’S not often you see a car creep down a long, steep set of stairs. It’s even less often that you see a car climb the same set of stairs backwards. Such is the ability of the G300, the seemingly impossible becomes the merely mundane.

The G300 CDI is a single-cab-chassis 4x4 that will serve a narrow sub-section of customers who sought the car out themselves, rather than waiting for a car company to come to them with the right product.

Those customers, who work in environmental protection, rural fire services and other companies where remote vehicular access is a prerequisite, spend their days in difficult, rough terrain.

They need a vehicle that not only can get in and out of situations that would make a stock Toyota LandCruiser cower in fear, but can carry a payload that’s almost equal to said LandCruiser.

The G300 is built atop the same chassis – known as the BR461 – that underpins the Mercedes-Benz G-Wagons that are built for the Australian Defence Force (ADF). In fact, the entire driveline, including the 135kW, 400Nm 3.0-litre V6 turbo, three diff locks and five-speed automatic transmission, can be found underneath the ADF vehicles.

It has a payload of 2085kg (minus the weight of whatever tray is fitted to the chassis) and a braked towing capacity of 2120kg. While the tow figure looks anaemic compared to the Hollywood numbers of the Ford Rangers and Holden Colorados of the world, both of those utes combined can’t carry as much stuff into the wild as a single G300.

Its design dates back 40 years to the original G-Wagen line, and Australia is currently the only market in the entire world to take a 461-based cab-chassis.

And the aforementioned customer base loves it. There is not another vehicle out there that can take two blokes, 650 litres of water and a host of equipment into the toughest terrain imaginable and make it back again.

Climb aboard the G300, and the sparseness is quite astonishing. Rubber mats reminiscent of the leftover bin at Clark Rubber, manual window winders, slabs of steel where trim usually resides. This is a Merc?It is, and it’s brilliant at its job.

It might be an old nail in design terms, but the massively oversized box section chassis, the trio of locking diffs and a set of off-road numbers to give a mountain goat pause gives the G300 an air of dignified indestructability.

It wades through water that covers the exhaust and laps at the base of the windows (650mm to be precise), clambers up slopes that can’t be walked up, and ratchets down hillside ‘roads’ with disdainful nonchalance.

It’s not the easiest thing to drive, with three buttons to operate the diffs, and more buttons to control the high- and low-range gearbox. All the while, you are being flung bodily around inside a steel-line jumping castle with corners and edges everywhere, and wrestling with heavy, meaty steering and diffs that are keen to let you know just how hard they are working by giving your shoulders a real workout.

The vinyl seats, though, are surprisingly supportive, even when being shaken like an espresso martini gone bad. They’re not pneumatically sprung, but they are not far off.

If you can hang on, the limits of the G300 are only bound by your own sense of mortality. At one point, I thought we were going over, such was the angle of a particular descent, and I instinctively braced for a roll that – of course – didn’t happen.

This ability, too, comes the old-fashioned way, via locked diffs and low-range gearing and not with electronic intervention. There is no hill descent control or anything of the sort. There is a hand throttle that can add steady-state movement in extremely rough terrain, and switchable traction control, but only two airbags and the skill of the driver will help in a sticky situation.

Mercedes will not sell many of these, and few will make it past the borders of a national park or working forest. But in its element, the G300 is the vehicle of choice for those who rely on that vehicle for their wellbeing.