In the late 1940s, Buster Peterson decided two Cats were better than one and created the “Twin D8”

As far as anyone knows, none of those original Twins is around today. 

Thanks to some antique Caterpillar lovers, the latter generations of Peterson Cat leadership and some really talented technicians, the Twin D8 was recreated in 2013.

https://www.equipmentworld.com/vintage-equipment/article/15752354/1950s-cat-twin-d8-two-dozers-joined-behind-one-big-blade