In general, the differences between the Beaufort and Beaufighter were minor. The wings, control surfaces, retractable landing gear and aft section of the fuselage, were identical to those of the Beaufort, while the wing center section was similar apart from certain fittings. The bomb-bay was dispensed with, and a forward-firing armament of four Hispano 20 mm cannons was mounted in the lower fuselage area. (These initially were drum-fed cannon, necessitating the radar operator having to manually change the ammunition drums—an arduous and unpopular task, especially at night and in the midst of a chase with a bomber target.) The areas for the rear gunner and bomb-aimer were removed, leaving only the pilot in a smoother, fighter-type cockpit. The navigator/radar operator sat far to the rear in a small bubble where the Beaufort's dorsal turret had been located.

The Bristol Taurus engines of the Beaufort would not be sufficient for a fighter and were replaced by the more powerful Bristol Hercules. This extra power presented problems with vibration. In the end they were mounted on longer, more flexible struts, which stuck out from the front of the wings. This had the side effect of moving the centre of gravity (CoG) forward, generally a bad thing for an aircraft design. It was then moved back into place by cutting back the nose area, which was no longer needed for the bomb-aimer in the fighter role. This put most of the fuselage behind the wing and moved the CoG back to where it should be, leading to the Beaufighter's famous stubby appearance.

Production of the Beaufort in Australia, and the highly successful use of British-made Beaufighters by the Royal Australian Air Force, led to Beaufighters being built by the Australian Department of Aircraft Production (DAP), from 1944 onwards. Australian-built examples are generally known as the DAP Beaufighter. The DAP's variant was an attack/torpedo bomber, known as the Beaufighter Mark 21: design changes included Hercules CVII engines, a dihedral tailplane and enhanced armament.

By the time British production lines shut down in September 1945, 5,564 Beaufighters had been built in England, by a number of manufacturers as well as Bristol: Fairey Aviation, (498) MAP (3336) and Rootes Securities Ltd (260).

When Australian production ceased in 1946, 365 Mk 21s had been built.

Operational service - Source: Wikipedia
By fighter standards, the Beaufighter Mk I was rather heavy and slow. It had an all-up weight of 16,000 lb (7,000 kg) and a maximum speed of only 335 mph (540 km/h) at 16,800 ft (5,000 m). Nevertheless this was all that was available at the time, as the otherwise excellent Westland Whirlwind had already been cancelled due to production problems with its engines.

The Beaufighter's main claim to fame would be that it was coming off the production lines at almost exactly the same time as the first British airborne radar sets. With the four 20 mm cannons mounted in the lower fuselage, the nose could accommodate the radar antennas, and the general roominess of the fuselage enabled the AI equipment to be fitted easily. Even loaded down to an even heavier 20,000 lb (9 t), the plane was still fast enough to catch the even slower German bombers. By early 1941, it was an effective counter to Luftwaffe night raids. The various early models of the Beaufighter soon commenced service overseas, where its rugged build and reliability soon made the aircraft popular with its crews.

A night-fighter Mk VIF was supplied to squadrons in March 1942, equipped with AI Mark VIII radar. As the faster de Havilland Mosquito took over in the night fighter role in mid to late 1942, the heavier Beaufighters made sterling contributions in other areas, such as anti-shipping, ground attack and long-range interdiction in every major theatre of operations.

In the Mediterranean, the USAAF's 414th, 415th, 416th and 417th Night Fighter Squadrons received 100 Beaufighters in the summer of 1943, achieving their first victory in July 1943. Through the summer the squadrons conducted both daytime convoy escort and ground-attack operations, but primarily flew defensive interception missions at night. Although the Northrop P-61 Black Widow fighter began to arrive in December 1944, USAAF Beaufighters continued to fly night operations in Italy and France until late in the war.

By the autumn of 1943 the Mosquito was available in enough numbers to replace the Beaufighter as the primary night fighter of the RAF. By the end of the war some 70 pilots serving with RAF units had become aces while flying Beaufighters.

Coastal Command began to take delivery of the up-rated Mk VIC in mid 1942. By the end of 1942, Mk VICs were being equipped with torpedo-carrying gear, enabling them to carry the British 18-inch or the US 22.5-inch torpedo externally. The first successful torpedo attacks by Beaufighters came in April 1943, with No. 254 Squadron sinking two merchant ships off Norway.

The Hercules Mk XVII, developing 1,735 hp at 500 feet was installed in the Mk VIC airframe to produce the TF (Torpedo Fighter) Mk X - commonly known as the "Torbeau." The Mk X became the main production mark of the Beaufighter. The strike variant of the Torbeau was designated the "Mk XIC." Beaufighter TF Xs would make precision shipping attacks at wave-top height with torpedoes or rockets. Early models of the Mk Xs carried ASV (air-to-surface vessel) radar, but this was replaced in late 1943 by AI Mark VIII radar, housed in a "thimble-nose" radome, enabling all-weather and nighttime attacks.

The North Coates Strike Wing (Coastal Command) developed attack tactics combining large formations of Beaufighters on anti-flak suppression with cannon and rockets while the Torbeaus attacked on low level. These tactics were put into practice in mid 1943 and in a 10 month period 27,000 tonnes of shipping were sunk. Tactics were further adapted when shipping was moved from port during night hours.

The Coastal Command RAF North Coates Strike Wing operated as the largest anti-shipping force of the Second World War, and accounted for over 150,000 tons of shipping and 117 vessels for a loss of 120 Beaufighters and 241 aircrew killed or missing. This was half the total tonnage sunk by all strike wings between 1942-45.

Pacific War - Source: Wikipedia
The Beaufighter arrived at squadrons in Asia and the Pacific in mid-1942. It has often been said — although it was most probably a propaganda invention — that Japanese soldiers referred to the Beaufighter as "whispering death", supposedly because attacking aircraft often were unheard (or seen) until it was too late.

South East Asia - Source: Wikipedia
In the South-East Asian Theatre, the Beaufighter Mk VIF operated from India on night missions against Japanese lines of communication in Burma and Thailand. The high-speed, low-level attacks were highly effective, despite often atrocious weather conditions and the makeshift repair and maintenance facilities.

South West Pacific - Source: Wikipedia
Before DAP Beaufighters arrived at Royal Australian Air Force units in the South West Pacific theatre, the Bristol Beaufighter Mk IC was employed in anti-shipping missions. The most famous of these was the Battle of the Bismarck Sea in which they co-operated with USAAF A-20 Bostons and B-25 Mitchells. No. 30 Squadron RAAF Beaufighters flew in at mast height to provide heavy suppressive fire for the waves of attacking bombers. The Japanese convoy, under the impression that they were under torpedo attack, made the fatal tactical error of turning their ships towards the Beaufighters, leaving them exposed to attack by the Allied medium bombers. Eight transports and four destroyers were sunk for the loss of five aircraft, including one Beaufighter.

Postwar - Source: Wikipedia
From late 1944, RAF Beaufighter units were engaged in the Greek Civil War, finally withdrawing in 1946.

The Beaufighter was also used by the Portuguese Air Force, as well as the air forces of Turkey and the Dominican Republic. It was used briefly by the Israeli Air Force.

Beaufighter Mk IC
The "C" stood for Coastal Command variant; many were modified to carry bombs.

Beaufighter Mk II
However well the Beaufighter performed, the Short Stirling bomber program by late 1941 had a higher priority for the Hercules engine and the Rolls Royce Merlin XX-powered Mk II was the result.

Beaufighter Mk IIF
Production night fighter variant.

Beaufighter Mk III/IV
The Mark III and Mark IV were to be Hercules and Merlin powered Beaufighters with a new slimmer fuselage carrying an armament of 6 cannon and 6 machine guns which would give performance improvements. The necessary costs of making the changes to the production line led to the curtailing of the Marks.

Beaufighter Mk V
The Vs had a Boulton Paul turret with four 0.303 machine guns mounted aft of the cockpit supplanting one pair of cannons and the wing-mounted machine guns. Only two Mk Vs were built.

Beaufighter Mk VI
The Hercules returned with the next major version in 1942, the Mk VI, which was eventually built to over 1,000 examples.

Beaufighter Mk VIF
This variant was equipped with AI Mark VIII radar.

Beaufighter Mk VI (ITF)
Interim torpedo fighter version.

Beaufighter TF Mk X
Two-seat torpedo fighter aircraft. The last major version (2,231 built) was the Mk X, probably the finest torpedo and strike aircraft of its day.

Beaufighter Mk XIC
Built without torpedo gear for Coastal Command use.

Beaufighter Mk 21
The Australian-made DAP Beaufighter. Changes included Hercules CVII engines, a dihedral tailplane, four 20 mm in the nose, four Browning .50 in the wings and the capacity to carry eight five-inch High-Velocity Aircraft Rockets (HVAR), two 250 lb bombs, two 500 lb bombs and one Mk13 torpedo.

Beaufighter TT Mk 10
After the war, many RAF Beaufighters were converted into target tug aircraft.