The first and original 'Caterpillar' or 'walking' engine made by R. Hornsby & Sons of Grantham. R. Hornsby & Sons grew into a major manufacturer of agricultural machinery, at their Spittle Gate Works. The firm went on to produce steam engines used to drive threshing machines and other equipment such as traction engines; their portable steam engine was one of their most important products and the market leader. Later a chain-track was added to an oil-engined tractor: the caterpillar track; these were developed and patented by Hornsby's chief engineer (and managing director), David Roberts, from July 1904. These were first used on tractors which served with the British Army towing artillery from 1910, but were later fitted to tanks which were used in the First World War from 1916. In 1909, a development model called the Little Caterpillar was demonstrated to the War Office. The army officers present at the demonstration believed it would frighten the horses!