In the early 1920s, the rounded hood and radiator used since 1915 were replaced by a handsome new gable hood and radiator. The basic types included:
- Model “K”, four-cylinder engine, 750 gpm piston pumper built between 1915 and 1926.
- Model “M”, six-cylinder engine, 750 gpm pumper produced between 1916 and 1933.
- Model “N”, six-cylinder engine, 1000 gpm pumper, more than 250 of which were delivered between 1917 and 1935.
- Model “P”, six-cylinder engine, six-piston 1300 gpm, 23 of which were delivered between 1919 and 1929.
- Model “J”, 750 gpm pumper powered by the smaller 4-3/4 x 6-1/2-inch six-cylinder engine, built between 1919 and 1930.
Typically, Model N-S-2 was a 1000 gpm piston pumper powered by the Ahrens-Fox six-cylinder motor of 5-1/2 inch bore and six-inch stroke, without booster or chemical equipment. The letter “S” indicated shaft-drive. The N-S-3 was equipped with a chemical tank and N-S-4 a booster tank system. In 1927 Ahrens-Fox delivered a special 1000 gpm high pressure pumper to the New York City (FDNY) Fire Department. The H-P-2 with six-piston pump delivered two powerful streams to the top of the 782-foot high Woolworth Building.
Ahrens-Fox H / J / K / M / N / P series 2 with closed cab