Sundstrand was manufacturing the Responder hydromechanical transmission for use in large trucks. It was designed as a replacement for the normally used 10-speed manual gearbox. The transmission was most useful for in-city and construction work service where slower stop-and-go driving makes an automatic transmission attractive.

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The Responder was capable of handling 250 hp, and weighs about 725 pounds. It had two modes of operation: (1) a straight hydrostatic mode for low speeds, and (2) a power-split mode for higher speeds. (At the lower end of the power-split mode, there was power recirculation through the hydrostatic path.)