In 1924, the company left Alexandra Park Aerodrome in south Manchester where test flying had taken place since 1918; the site was used for a mixture of recreation and housing development. A rural site to the south of the city was found at New Hall Farm, Woodford in Cheshire, which continued to be used by aviation company BAE Systems until March 2011; the site has now been earmarked for a mixed use development. In 1928 Crossley Motors sold AVRO to Armstrong Siddeley Holdings Ltd. In 1928 A.V. Roe resigned from the company he had founded and formed the Saunders-Roe company, which after World War II developed several radical designs for combat jets, and, eventually, a range of powerful hovercraft. In 1935 Avro became a subsidiary of Hawker Siddeley. Maintaining their skills in designing trainer aircraft, the company built a more robust biplane called the Avro Tutor in the 1930s which the Royal Air Force (RAF) also bought in quantity. A twin piston-engined airliner called the Anson followed but as tensions rose again in Europe the firm's emphasis returned to combat aircraft. The Avro Manchester, Lancaster, and Lincoln were particularly famous Avro designs. Over 7,000 Lancasters were built and their bombing capabilities led to their use in the famous "Dam Busters" raid. Of the total, nearly half were built at Avro's Woodford (Stockport) and Chadderton (Oldham) sites, with some 700 Lancasters built at the Avro "shadow" factory next to Leeds Bradford Airport (formerly Yeadon Aerodrome), northwest Leeds. This factory employed 17,500 workers at a time when the population of Yeadon was just 10,000. It was the largest building in Europe at the time, at , and its roof was disguised by the addition of fields and hedges to hide it from enemy planes. The old taxiway from the factory to the runway is still evident. The Avro Lancaster carried the heaviest bomb loads of the war, including the Grand Slam bomb. The civilian Lancastrian and maritime reconnaissance Shackleton were derived from the successful Lancaster design. The Tudor was a pressurised but problematic post-war Avro airliner which faced strong competition from designs by Bristol, Canadair, Douglas, Handley Page, and Lockheed. With the same wings and engines as the Lincoln, it achieved only a short (34 completed) production run following a first flight in June 1945 and the cancellation of an order from BOAC.