Tom ford tests the worlds ultimate 4x4, the Unimog

It's no ordinary car, it's a Unimog, a Mercedes off-roader that is almost as unknown as the Navy special forces that use them. This is the top-of-the-range U500, which they use for specialist haulage in conditions that would leave a 4x4 absolutely floundering and where a tractor would make you duck. The Unimog costs around £90,000, not bad for something that looks like a pitbull crossed with a lorry. About 100 a year gets sold in the UK, it's not just to military utility companies who buy them; they're famed for being indestructible and incredibly reliable, useful qualities when you're working in the middle of nowhere or trying to round up Al-Qaeda before tea.

Most custo custers for special equipment like this tend to offer suggestions for improvements they'd like to make, but the SPs basically just turned around and said we'd like to buy some more to figure out why the Special Boat Service love these things so much. I want to take the same sort of driving lesson as they do, and for that, I need a man called Derek. Derek Owen is the technical Guru for Unimog in the UK, and he's going to teach me just like he teaches the SBS.

Hello Tom, good morning, it's quite a way up here. So Derek, what are the main controls right now? This is the steering wheel, yeah, yeah. Now we can skip that, right, okay, let's move on. We've got 16 forward and 14 reverse gears with this gearbox. Um eight on the selector here, and then we can actually engage a low range here; they're what we call working gears, okay? I know this has got a straight six engine, so it's a 286 brake horsepower which is the same as a BMW 635d. It's got one 1.10 Newton metre of torque, which is the same as a planet, yeah, with this type of vehicle, it's torque that's much more important in many ways than horsepower.

I think we should see how much that torque counts right. I'm going to start her up, okay, let's go for this hill. We want to be in third gear and then drive it up; I don't think I can walk up this do crank it so. This is really muddy, really muddy, in quite steep. Can't see anything now, I'm just looking at Sky, that's like driving a tank right. This is a really steep drop here, and we need to be in second gear with the diff locks in because it's as important to have the diff locks in going down. Oh Christ, just so, just come off the pedals; you'll need to cover the brake and break it a little bit while we go.

I'm just hanging out the seat belts here, that's odd, a little slip there but little bit, it's moving all over the place doing a fairly sharp left here. So far, so good, but the Unimog has some party tricks that set it apart where most 4x4s would drown. The Unimog wades and when things get slippery, it can rely on something other than its permanent four-wheel drive for traction. Um, what does this button do? Right, this Unog's got a central tire inflation system which allows us to raise and lower the tire pressures to suit the ground conditions.

Okay, so by pushing this button in the up position, we're putting the pressures up, and then we can lower the pressures by putting the switch. So what would you use that for? Then, in really wet conditions, you can increase traction by as much as 30% by lowering the pressures to something like 1.5 bar. It's undeniably talented off-road, and you can see why the Special Forces like them. But the real reason a Unimog is unique is that this heavy-duty 12-ton off-roader is also capable of 55 mph on road, although a version has just shown up on our radar that does 65 M an hour, and we've tracked it down.

I'm excited to be here, it's the maddest thing we've ever had in the car park. This is the 100,000 Mercedes-Benz Unimog Black Edition fettled by Brabus; this is the biggest rollover hoop I've ever seen. It's got upswept exhaust and inside, it's all leather and carbon fiber, and it's got the command system from Merc's S-Class. It rocks, does work, but what is it for? Well, the brochure says um special occasions, but unsurprisingly, it's originally made for people in the Gulf region where you know a Rolls-Royce Phantom's 10 a penny and a Hummer's just not hard enough.

Also, where there aren't enough cars that can carry 4 tons at 65 mph off-road.