In the 1940's and 1950's, there were several tracked landing gear systems developed for the purpose of allowing landing on soft ground and/or using particularly heavy aircraft such as the B-36. For the first half century of manned flight, landing gears overwhelmingly had only a single, large wheel per leg. This was the cheapest and simplest way to ensure ground mobility, but ran into trouble when aircraft grew in size. When the XB-36 prototype started testing in 1946, only three airfields in the US were able to tolerate the 156 psi pressure of its single main wheels.For operating from unprepared surfaces, tracked gears were the straightforward transfer from tank experience to landing gear design.
However, another route which was tried at about the same time was to increase the number of wheels the aircraft rests upon. With hindsight, the multi-wheel way was the better solution and has prevailed. When used with large, low-pressure tires it does not exert significantly more ground pressure than a tracked gear.
A couple of youtube clips.
A-20 testing
https://www.youtube.com/watch?v=X9vmamugkI4XB-36
https://www.youtube.com/watch?v=eDCgMlomhvMBelow A few photos of the Convair XB-36 with experimental tracked landing gear, to reduce ground pressure for soft-field use. The original B-36 landing gear consisting of a giant tire weighed way more than the tracked version and was such a point load that the gear was prone to sink right thru any but the thickest concrete of the day. The B-36 was actually designed before WWII but was completely impractical because there was no landing gear that could support it and no engines powerful enough to lift it. That changed after the war with the P&W R4360 engine of 4000+ HP and new tire technology. However the idea of one main gear wheel was from the '30s and soon the main gear had 4 wheels of smaller size.
![Image](https://farm2.staticflickr.com/1823/29285840508_e3cb8e6bb6_h.jpg)
![Image](https://farm2.staticflickr.com/1786/29285838128_9f1739d1aa_h.jpg)
![Image](https://farm2.staticflickr.com/1809/29285821118_1a8235f88f_h.jpg)
![Image](https://farm2.staticflickr.com/1830/41346364030_46c5b0c840_h.jpg)
![Image](https://farm1.staticflickr.com/914/42253057625_9180c7421d_h.jpg)
![Image](https://farm2.staticflickr.com/1822/29285837098_acf3aca35d_h.jpg)
![Image](https://farm2.staticflickr.com/1788/42438896124_ec3d19301f_h.jpg)
![Image](https://farm2.staticflickr.com/1764/29285817928_771dab7670_h.jpg)
![Image](https://farm2.staticflickr.com/1761/29285819558_a59fa11a10_h.jpg)
![Image](https://farm2.staticflickr.com/1828/29285833888_e6d1a14a65_h.jpg)
![Image](https://farm1.staticflickr.com/925/43156899241_046b46d0ac_h.jpg)