Developed from the Type 142 light transport and ordered directly off the drawing board, the Bristol Blenheim was quite remarkable in being the fastest RAF aircraft at the time of its service entry, easily outpacing the biplane fighters which were prominent at the time. Despite this impressive introduction, it soon because obsolete as newer, faster monoplanes were introduced, and as a consequence, suffered heavily during the initial campaigns of the war, notably the Battle of Britain. Fortunately it proved very capable as a light bomber (mostly in the Mediterranean, North Africa, and the Far East) and especially as a night fighter where it became the mainstay of the RAF until 1941. Its notable accomplishments include being the first large-scale application of Airborne Intercept (AI) radar and the first successful radar interception of the war. Foreign operators included Canada, France, Finland, Greece, Hungary, Portugal, Romania, South Africa, Turkey, and Yugoslavia.

The prototype Type 142M (originally designed for newspaper magnate Lord Rothemere as a fast executive transport) flew on 25 June 1936 and entered service as the Mk. I in early 1937. This was a standard light bomber version, it was followed by the Mk. IF day and night fighter conversion, similar to its predecessor except for the deletion of the bomb bay. In daylight operations it was found to be extremely vulnerable and suffered at the hands of the more agile German and Japanese single-engined fighters in the early campaigns. Nevertheless as a night fighter it was extremely effective at a time where more advanced aircraft were not yet available. Next in production was the Mk. IV, used by Bomber Command and also Coastal Command which used it rather successfuly for anti-ship strike. Sub-variants included the Mk. IVF fighter and the Mk. IVL long-range conversion. Lastly, the Mk. V was a high-altitude bomber for use in North Africa which met with poor success on account of their vulnerability.