Mike Cross aims for the gap in the trees, and guns it. There's a muted snarl from the 395-hp straight-six under the hood, the hiss of rubber on wet gravel and the whoomp! whoomp! whoomp! of muddy water exploding from potholes. Cross is slouched in the driver's seat, relaxed but eyes laser-focused as he waltzes 5,035 pounds of SUV through mud-slicked corners with deft, minimalist movements of the steering wheel, his right hand periodically making the short reach across to the high-mounted shifter to grab another gear.

The road straightens, and Jaguar Land Rover's chief engineer, vehicle integrity, buries his right foot. We hit 100 mph, hovercrafting over the cratered surface on the long-travel air suspension. Then it's hard on the brakes and three quick snicks of the stubby shifter, ready for the rapidly approaching 90-degree corner. Off the brakes, turn-in, and on the power. The big SUV slides gracefully for a moment before being collected with a quick flick of the wrists. The four-wheel-drive system digs through the surface slush and propels us toward the next corner.

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We hit 100 mph. And in a Land Rover Defender, no less; the all-new, 2020 model year long-wheelbase 110, powered by JLR's new turbocharged, mild-hybrid 3.0-liter engine, to be precise. In the high-spec HSE model I'm riding in, which stickers at $69,375, it has an eight-speed automatic transmission, computer-controlled all-wheel drive, height-adjustable air suspension with variable rate shocks, 20-inch alloy wheels, adaptive cruise control, and a nice comfy interior with heated leather seats, climate control, and a state-of-the-moment infotainment system.

This ain't your daddy's Defender …

I learned to drive in one of those, my old man's 1960 Land Rover Series II, foxed and faded Army green paint inside and out, a raggedy canvas top that flapped like a tent in a hurricane at 30 mph, and no syncro on first or second gears. It could pretty much go anywhere. Anywhere but 100 mph, that is, unless you drove it off a cliff. I loved that old Series II, though, and I still lust after one, but as something to take out and drive when I have nowhere to go and all day to get there. Noisy and clunky and slower than a wet weekend in Cleveland, with off-on drum brakes all round, and a hair-trigger clutch and steering that had you grunting with effort, it would be utter misery as everyday transport.

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The previous-generation Defender, out of production since early 2016, wasn't a million miles removed from that crude old Series II. Sure, it had a nice torquey diesel four-banger under the hood, a six-speed manual transmission with synchromesh on all the gears, a sophisticated permanent all-wheel-drive system, plus smooth-riding coil springs and disc brakes all round. But it felt older than Methuselah the moment you wheeled it into traffic. Like a Morgan Plus 4, the old Defender was an automotive curio; a time-warp machine whose olde worlde quirks had survived simply because it had been quietly parked up a developmental cul-de-sac while the modern world drove by. Truth be told, it was a noisome, tiresome thing to drive any great distance.

It would be easy to criticize the 2020 Defender as too heavy, too complex, too expensive. If you put on rose-colored glasses and just look at the numbers it seems a valid criticism, but as my ride with Cross proved, this new Defender is much more rounded and accomplished, more able to do more things more competently, more efficiently, more safely than the quirky old one ever could. How? An intelligently rendered combination of hardware and software, that's how.

The new Defender rolls on an architecture called D7x, which is basically a toughened and strengthened version of the D7u architecture used by the Range Rover and Range Rover Sport. And it debuts JLR's most advanced electronic architecture and infotainment interface yet, with always-on 4G and 5G, plus voice activation and over-the-air-software upgrade capability. "It was a given that the car had to be the best car available off-road," Cross says, "but once that was achieved—through the hardware, really—we wanted to make the car as good as it could possibly be on-road."

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The new Defender has a very stiff all-aluminum monocoque structure—10 times stiffer than average body-on-frame off-roader, and three times stiffer than the best, says JLR engineering chief Nick Rogers—and suspension components, though significantly strengthened, with which Cross and his development engineers were deeply familiar. "The most interesting challenge was developing the car's driving character," he says. "I wanted it to drive like it looks. I wanted it to feel like an analog car even though it has many digital systems, to have this connected, robust feel."

The Defender's deep digital neural network allowed Cross and his team to dial in the on-road dynamic capability they wanted while keeping the off-road capability that is core to the Defender brand. The main engineering compromise was over the amount of wheel travel. "More is better off-road, but that has a direct consequence to body roll on-road," says Cross, who concedes the more hardcore off-roaders on the team probably would have preferred a touch more travel to improve articulation in extreme off-road situations. But once the team had agreed what the wheel travel would be, Cross says, it was simply a matter of tuning.

By modern SUV standards the Defender feels relatively soft and plush, and it rolls through corners. But there's a majestic grace to it all, not unlike that of an old-school Range Rover, though much more deftly controlled. We took a few hot laps of the tarmac test roads at Gaydon, at one point taking the Defender through a fast, greasy sweeper at just over 100 mph, gently teasing the excellent Pirelli Scorpion Zero all-season tires to the edge of their traction coefficient. As Cross demonstrated, the Defender has none of the lumbering three-wheeling comedy act you get when pushing a Mercedes-Benz G-Class through tight, high-traction corners.

"Roll is fine as long as the roll damping is well calibrated," says Cross, who started his automotive career as an apprentice at Land Rover 44 years ago but, ironically, has spent most of it honing the ride and handling of fast Jaguar sedans and sports cars. "I think the driver probably feels the rate of roll more than the roll angle."

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Nostalgia isn't what it used to be. JLR knows that for it to be a sales success, the 2020 Defender must not only be an SUV with character and capability that pays homage to its past. It must also, more important, offer all the comfort and usability today's consumers expect. "It was a given it had to be the best off-road," Cross says, "but once that was achieved, we wanted to make the car as good as it could possibly be on-road so it was easier to live with."