What series introduced differential steering?

I don't know all of the first of each series, the following is a start, D6H, D7H, D8N, D9R.

I had a wheat farming friend near Narromine NSW, during a wet year in the Sixties used an Oliver to get their crop in, they had two 660 International wheel tractors that they had to leave in the shed and double shifted the Oliver. Early Oliver's were diff steering of sorts, they had a diff and steering was by applying brake to one side. He said it was good to follow a line as correction was achievable whilst maintaining drive on both tracks.

Wombat

Thanks Wombat, I'm a little surprised that I haven't found a youtube of someone ploughing with one. I watch the Italian videos and they're as jerky as heck trying to stay on course and I figured a diff steer would be an ideal application (if one was to use a steel-tracked tractor)

Hi Team,
does not answer your question directly but the link below is a brief description of the system in use from 2011.
I would be guessing to say if or not the system has changed as it worked well and was smooth to operate in my experience around the Dealer shop and surrounds of the test area.

https://www.youtube.com/watch?v=A5_iNL9q18Y&ab_channel=Cat%C2%AEProducts

Cheers,
Eddie B.

Thanks Eddie, I looked at that one and about three others figuring out which components are connected to others. One guy made a model where the incoming bevel drive drove the planetary carrier for the center planetary, and the three sun gears are all on the same shaft, with the steering motor driving the right side ring gear. I can't tell if this is the same design as Cat's but I imagine it can't be too far different. Other designs have only two planetaries and the steering motor drives the two ring gears in opposite directions - seems like a simpler system than the three planetary system. Did the engineers ever state how much power it takes to run the steering motor (would differ for different models of course)?