In 1943, the United Kingdom worried by the increase of German submarine operations in the Atlantic, requested and obtained permission to operate anti-submarine aircraft from Terceira Island at Azores, Portugal, which was done from the end of 1943 with the RAF 247th Group from Lajes airfield, built meanwhile.
Due to the granting of these facilities a steady flow of aircraft was sent from England to Portugal as part of payment, and also considering the existing alliance between the two countries since 1373.
Among several British aircraft, twenty five Bristol Blenheims, being twenty two MkIVs and three MkVs, were sent to join both the "AeronŠutica Militar" (army), and "AeronŠutica Naval" (navy). Despite the replacement of the navy Blenheims by Beaufighters in 1945, they continued in service until 1952.
The MkIV modelThe Mk.IV variant had a crew of 3, and used the 995hp Bristol Mercury XV radial engine. These engines gave it a maximum speed of 266 mph (428km/h), a ceiling of 27,280 ft (8300m) and a range of 1,215 mi (1810 km). The ground attack version mounted 5 machine guns and could also carry 1,325 lbs of bombs. It had the standard single machine gun in the port wing, a pair of rear firing 0.303 machine guns in a chin blister and a pair of machine guns in the rear turret. The Mk.IVF (fighter/attack plane) carried six 0.303 machine guns, four in a belly pack, 1 in the port wing and 1 in the rear turret.
The MkV modelThe Mk.V variant was the last in the line using the Bristol Mercury XXX radial engine with 950 hp (708 kW). This engine did not increase the speed at all, but gave it a ceiling of 31,000 ft (9450 m) and a range of 1600 miles (2575 km).
Blenheims built in Canada used the name "Bolingbroke".