On 7 May 1940, the first production Stirling, conducted its first flight. According to Norris, initial rates of production were disappointing, and were in part due to delays in the delivery of machine tools and forgings. It has also been alleged that production of the Stirling was negatively impacted by a decision by Lord Beaverbrook, the Minister of Aircraft Production, which had ordered a change in priority from four-engined bombers towards fighters and twin-engined aircraft to replace those lost during the Battle of Britain. In August 1940, series production of the Stirling commenced at the Rochester factory.