In early 1939, the first batch of Blenheim Mk IVs were accepted into service; these lacked outer fuel tanks but were accepted due to the urgent demand for the type. Early Blenheim Mk IVs were also equipped with the Mercury VIII engine, most were fitted with the more powerful Mercury XV or Mercury 25 models. Further aircraft deliveries were made to the production standard and were primarily manufactured by Avro and Rootes. Production of the Blenheim IV continued until June 1943, when newcomers such as the Beaufort-derived Beaufighter had succeeded the type. A total of 3,307 were produced.