In Britain, David Roberts of Richard Hornsby & Sons had attempted starting in 1911 to interest British military officials in a tracked vehicle, but failed. Benjamin Holt of the Holt Manufacturing Company bought the patents related to the "chain track" track-type tractor from Richard Hornsby & Sons in 1914 for £4,000. 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. The British War Office conducted trials with Holt tractors at Aldershot but saw them only as suitable for towing heavy artillery.