At the start of World War I, Cox & Co employed some 180 staff, of which one third joined the army. During the war some 250,000 men were on their books, 50,000 cheques were cleared a day and a special department was set up to deal with the influx of American soldiers in 1917. By the end of the war, some 4,500 people worked for the firm. Cox & Co suffered a downturn in business as a result of the end of the war in 1918.