Hall helped Jesse G. Vincent of Packard design the famous Liberty airplane engine, which has a number of features that are discernibly Hall-Scott.

The designs he specified gave Duesenberg an immediate advantage and were quickly copied and applied to all high-speed engines using poppet valves, which continued to the present day.

The company survived the Depression and then attained its highest production rates and employment numbers in World War II by building engines for a variety of military products, including a tank retriever, the M-26/M-26A1, and the Higgins boat (LCVP).

Some post-World War II ACF-Brill buses manufactured in Philadelphia and purchased by Greyhound and Trailways were equipped with Hall-Scott engines.

This had little effect on the bottom line, and so in 1958 Hall-Scott sold its engine division to Hercules Motors Corporation and closed the Berkeley plant.

Two Hall-Scott interurban coaches from the former Sacramento Northern Railroad (serial numbers 1019 and 1020) are at the Western Railway Museum at Rio Vista, California.

Nevada Copper Belt 21 (1910 100 hp) is stored "serviceable" at the California State Railroad Museum in Sacramento.