On April 22, 1918, British Army Col. Ernest Dunlop Swinton visited Stockton while on a tour of the United States. The British and French armies were using many hundreds of Holt tractors to haul heavy guns and supplies during World War I, and Swinton publicly thanked Holt and his workforce for their contribution to the war effort. During 1914 and 1915, Swinton had advocated basing some sort of armored fighting vehicle on Holt's caterpillar tractors, but without success (although Britain did develop tanks, they came from a separate source and were not directly derived from Holt machines). After the appearance of tanks on the battlefield, Holt built a prototype, the gas-electric tank, but it did not enter production.