 Complete the following phrase:  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 firms 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 