Prior to World War II, limitations in engine power required each desired military role to be filled with a custom aircraft. Engine power grew dramatically during the early period of the war, roughly doubling between 1939 and 1943. The Bristol Blenheim, a typical light bomber of the opening stages of the war, originally designed in 1934 as a fast, civil transport to meet a challenge by Lord Rothermere owner of the Daily Mail.It had two Bristol Mercury XV radial engines of 920 hp each and a crew of three. Its payload was just 1200 lbs of bombs.