When World War I began, Allison suspended racing, and the Allison Experimental Company began machining parts, tools, and masters for the Liberty airplane engine — the main power plant used in the US war effort. After the war, Allison entered a car in the 1919 Indy 500 and won. It was the last race Allison's team ever entered as he turned his company's attention to aviation engineering. The company's expertise in aviation was the major factor in General Motors decision to buy the company following James Allison's death in 1928.