Although the new design looked similar in most ways to the Blenheim, it was in fact somewhat larger, added another crewmember (to four), and was considerably heavier. The later proved too much for the Blenheim's Mercury engines, and so a switch to the larger Taurus engine was made. The Taurus proved to be a problem on the Beaufort, and overheating was a constant problem. This introduced delays into the production, so while the plane had first flown in October 1938 and should have been available almost immediately, it wasn't until December 1939 the production started in earnest, with service entry in August 1940.
A number of changes were introduced into the line, and after the 1014th had been delivered, all of these were collected into the new Mk.II. The Mk.II was different visibly primarily in the use of a flat bomb-aiming window under the nose. However it also included a second forward firing 303" gun in the wing, a blister under the nose with a rearward firing gun, an improved dorsal turret with a newer Vickers K gun, an installation of the ASV Mk.II air-to-surface radar, removal of the Youngman trailing edges, retractable tailwheel, and improved airflow on some points of the aircraft. Performance, sadly, was not improved.
Oddly the first 165 of the Mk.II's were delivered with the Pratt and Whitney Twin Wasp engines instead of the Taurus. The 166th on reverted to the Taurus, although the better performing and more common Twin Wasp seems like a much better fit for the aircraft. The Taurus engine was otherwise unused, and that production line could surely be put to better use.
The Beaufort was a slow aircraft, with a top speed of only 265mph, which dropped to a mere 225mph when carrying a torpedo. Although it did see some use in the torpedo bomber role, notably in attacks on the Scharnhorst and Gneisenau while in port in Brest, the Beaufort was more often used as a mine-laying aircraft while in European service. It saw considerable action in the Mediterranean theatre, where it helped put an end to Axis shipping supplying Rommel.
Coastal Command regarded the Beaufort as a failure, but it turned out to make an excellent basis for a heavy fighter in the form of the Bristol Beaufighter. The Beaufighter was so superior to the Beaufort that a number were specially modified to carry a torpedo, and it replaced the Beaufort in service.
In the Pacific war, however, the Beaufort played a vital role. With Britain's domestic aircraft industry working at capacity already in early 1939, the Air Ministry instigated negotiations to set up parallel production lines in Australia, to supply both the RAF and the RAAF with Beauforts and Twin Wasp engines. Australia's tiny industrial base was barely up to the task of making a modern aircraft, but frantic efforts saw the first of an eventual 700 roll off the line in August 1941. Japan entered the war soon after, swiftly removing the RAF from the Pacific theatre, and the need for modern aircraft in the South Pacific was desperate. With the United States unable to spare more than a few Kittyhawks, P-39s and Bostons, and the United Kingdom in yet worse position, the locally-produced Beaufort became the primary strike weapon of the RAAF in the first two years of the Pacific War. Production continued to increase, reaching almost one a day in 1943, and though inexperience and hurry combined to produce a horrendous accident rate early on, the Beaufort served with 19 squadrons and played a vital role in stemming the Japanese advance: as a maritime patrol aircraft, bomber, fighter-bomber, and most of all on maritime strike duties, where Beauforts sunk an impressive tonnage of merchant and naval shipping. After roughly 50 each of the Mk V, VI and VII and 520 Mk VIIIs, production ceased in favour of more modern types in 1944, and handful of Mk.VIII's were later modified as transports, known as the Mk.IX or 'Beaufreighter'.
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