When World War I broke out, with the problem of trench warfare and the difficulty of transporting supplies to the front, the pulling power of crawling-type tractors drew the attention of the military. In British trials, the Holt tractor was found to be better suited than its competitors to haul heavy loads over uneven ground. The War Office was suitably impressed and chose it as a gun-tractor. Holt Caterpillar tractors were also the inspiration for the development of the British tank, which profoundly altered ground warfare tactics.