The Cat D12: Myth, Legend… or a Very Australian Reality?

Photo: Mearns Hire

For years, heavy equipment circles have buzzed with the same tantalising question: Will Caterpillar ever build a D12 dozer? Bigger than the mighty D11, more powerful than anything currently roaming mine sites or job sites, the Cat D12 has lived mostly in rumours, pub talk, and online forums.

Officially, Caterpillar has never confirmed such a machine exists.

Unofficially? Queensland might beg to differ.

Some time ago, a series of photos circulating on Instagram caught the attention of earthmoving enthusiasts around the world. Shared by well-known machinery spotter Michael Bullock — better known as @the_english_earthmover — and originally taken by Lawrence Lowe, the images appeared to show something many believed only existed in rumour: a machine that looked remarkably like the mythical Cat D12 out in the wild.

As Bullock boldly put it: “D12s do exist!”
The catch? They’re only found in Queensland, Australia.

Built, Not Bought

Digging deeper reveals that these machines aren’t factory-built Caterpillars at all — but arguably something even more impressive.

The story leads to Mearns Hire, a Queensland-based contractor established back in 1965. Known for tackling some of the toughest land-clearing and rehabilitation work in Australia, Mearns Hire has never been content with off-the-shelf solutions. Their work — blade ploughing rock-hard outback soil, slicing through deep-rooted scrub, and re-seeding vast tracts of land — demands machinery that goes beyond standard specifications.

So they built it themselves.

Turning a D11 Into a Monster

The starting point is a Cat D11R or D11N — already one of the largest and most powerful dozers on the planet. But for Mearns Hire, “already massive” wasn’t enough.

Out goes the standard 850-horsepower V8 engine.

In its place? A Cat 3512 V12 engine, borrowed from a Cat 785 mining dump truck. To make it fit, the chassis is stretched, giving the dozer a longer frame and room to shoehorn in the giant powerplant.

The result is staggering: 1,250 horsepower — a full 400hp jump over the standard D11.

Remarkably, the original D11 transmission remains, paired with the dump truck’s torque converter and lock-up clutch system to handle the immense load. Cooling is managed with the standard radiator for engine coolant, while a secondary transmission oil cooler is mounted high atop the ROPS frame. It may look unconventional, but it’s essential.

Why? Because this beast spends its days grinding away in second gear, dragging a 10-metre-wide blade plough through unforgiving terrain for hours on end.

Aussie Ingenuity at Its Finest

This isn’t a marketing concept, a prototype hidden behind factory doors, or a speculative render online. These machines are real. Mearns Hire has reportedly modified four of them — all purpose-built for Australia’s harshest environments.

It’s hard not to agree with Bullock’s assessment: this is an extraordinary example of Australian engineering ingenuity. When the job demands more than the biggest machine available, Australians don’t wait for permission — they build what they need.

So, is the Cat D12 a myth or a legend?

Maybe officially it still is.
But out in the Queensland outback, pulling steel through hardpan and scrub, the legend is very much alive — and it’s wearing Caterpillar yellow.