卡特彼勒 的概念车或原型车

Buster Peterson combined two Cat D9Gs end-to-end to create a single pushloading tractor with twice the power, but for high-volume material handling with a crawler tractor, the issue wasn't so much the horsepower as it was blade capacity. Various experiments were attempted – and failed – in creating a more powerful, higher-capacity dozer by combining two large crawler tractors onto one undercarriage.

In 1969, the same year that Caterpillar Inc. introduced the Dual D9G for pushloading, it also introduced the S×S D9G. The concept was similar to the Dual D9G, but instead of end-to-end these worked side-by-side (S×S). The two tractors were physically connected with ball and socket joints at the rear and at the two inside crawlers, and they pushed a 24-ft. wide modified U dozer. The ball-and-socket joints provided optimum traction under load and on rough ground. The operator was stationed on the left-hand unit, as seen from the rear, and operated both machines through a joystick and air over hydraulic controls, with the control lines on the rear tie bar. The two tractors could be separated for individual use as needed.

The S×S D9G was rated at 770 hp.