From Appendix 12: Known for quality ground vehicles. In 1916, under the command of Parry Thomas, they designed a W18 aircraft engine, with three rows of 6 cylinders in vertical W. But it did not go into production.

-An 8-cylinder prototype of an X-engine was also designed and built. It is shown in the below photograph.

"8-cylinder X-engine from WWI, made by Leyland"