X engine

The 16-184 engine was installed in several hundred "subchaser" boats from 1941 onwards, where they were typically used in pairs.

From 1944 the similar 16-338 engine was produced for submarines, where four were used in each of the first four members of the USN Tang class.

These proved unreliable in service and were subsequently replaced by three Fairbanks-Morse engines in each boat.

[5] Several prototype 24-cylinder X engines for military aircraft were developed during World War II, including the Daimler-Benz DB 604, Rolls-Royce Exe and Isotta Fraschini Zeta R.C.

[6][7] During the 1960s, Honda is said to have experimented with an X-32 engine configuration for their Formula One racing efforts, but abandoned the design as being too complex and unreliable.