During World War I, the factory was focused solely on War Department production, producing petrol engines, lighting sets and munitions. Many of the men left for the front, meaning that a large portion of the workforce was female. After the war, Sir Robert Lister retired and turned management at Dursley over to his grandsons (sons of Charles Ashton Lister CBE) Robert, Frank, Percy and George together with A. E. Mellerup. Charles Ashton Lister managed the company's business in North America and was based in Canada. George managed home sales and Frank was in charge of buying, while Cecil did not have a clearly defined role at all, and, although Robert was the eldest, it was Percy (later Sir Percy) who had by far the most significant impact.