Lancaster B.I
The original Lancasters were produced with Rolls-Royce Merlin XX engines and SU carburettors. Minor details were changed throughout the production series – for example the pitot head design was changed from being on a long mast at the front of the nose to a short fairing mounted on the side of the fuselage under the cockpit. Later production Lancasters had Merlin 22 and 24 engines. No designation change was made to denote these alterations.

Avro Lancaster B Mark I, W4113 ‘GP-J’, of No. 1661 Heavy Conversion Unit based at Winthorpe, Nottinghamshire, in flight. W4113 was a veteran aircraft having flown on a number of raids with Nos. 49 and 156 Squadrons RAF in 1942 and 1943.
Avro Lancaster B Mark I, W4113 ‘GP-J’, of No. 1661 Heavy Conversion Unit based
at Winthorpe, Nottinghamshire, in flight.

[Source: Wikipedia]

Lancaster B.I Special
32 Aircraft were adapted to take first the super-heavy "Tallboy" and then "Grand Slam" bombs. Up-rated engines with paddle-bladed propellers gave more power, and the removal of gun turrets reduced weight and gave smoother lines. For the Tallboy, the bomb bay doors were bulged; for the Grand Slam, they were removed completely and the area faired over. For some Tallboy raids, the mid-upper turret was removed. This modification was retained for the Grand Slam aircraft, and in addition the nose turret was later removed. Two airframes (HK541 and SW244) were modified to carry a dorsal "saddle tank" with 1,200 gal (5,455 L) mounted aft of a modified canopy for increasing range. No. 1577 SD Flight tested the aircraft in India and Australia in 1945 for possible use in the Pacific, but the tank adversely affected handling characteristics when full and an early type of in-flight refuelling designed in the late 1930s for commercial flying boats was later used instead.

Lancaster PR.1
B 1 modified for photographic reconnaissance, operated by RAF No. 82 and No. 541 Squadrons, wartime. All armament and turrets were removed with a reconfigured nose and a camera carried in the bomb bay. The type was also operated by 683 Squadron from circa 1950 for photographic reconnaissance based at Aden and subsequently Habbaniya in Iraq until disbanded 30 November 1953.

Lancaster B.I (FE)
In anticipation of the needs of the Tiger Force operations against the Japanese in the Far East (FE), a tropicalised variant was based on late production aircraft. The B I (FE) had modified radio, radar, navaids, and a 400 gal (1,818 L) tank installed in the bomb bay. Most were painted with white upper-surfaces to reduce internal temperatures in the tropical sun, and black undersides with a low demarcation between the colours, completely omitting any red colours on the national insignia in all cases to avoid confusion with the hinomaru insignia of the Japanese.

Lancaster B.II
Bristol Hercules (Hercules VI or XVI engines) powered variant, of which 300 were produced by Armstrong Whitworth. One difference between the two engine versions was that the VI had manual mixture control, requiring an extra lever on the throttle pedestal. Very early examples were fitted with an FN.64 ventral turret; however, these were quickly removed due to problems with aiming the turret through its periscope (which prevented the gunner from seeing a target he was not already aiming at), and inadequate traverse speed.

Due to the Luftwaffe Schräge Musik attacks, a variety of unofficial field modifications were made, including fitting of 20 mm cannon or a .50 inch machine gun in the open hole where the FN.64 had been installed, before an official modification (Mod 925) fitted with a .303 inch machine gun was authorised for the same location, though not in all aircraft. These were rarely installed on other variants as the H2S radar that was not used on the B II was mounted there. Three types of bulged bomb bay were used on the B II, the prototype having a narrow bulge running from just aft of the cockpit to the end of the bomb bay, while early production examples had a full width bulge that ran the same length and on late production examples the bomb bay doors were prominently bulged throughout their length.

Lancaster B.III
This variant, which was built concurrently with the B I and was indistinguishable externally from that variant, was fitted with Packard-built Merlin engines. The Packard Merlins used Bendix – Stromberg pressure-injection carburettors, requiring the addition of slow-running cut-off switches in the cockpit.

Lancaster B III (Special)
Known at the time of modification as the "Type 464 Provisioning" Lancaster, 23 aircraft of this type were built to carry the "Upkeep" bouncing bomb for the dam busting raids. The bomb bay doors were removed and Vickers-built struts to carry the bomb were fitted in their place at Woodford Aerodrome near Stockport where the workers worked day and night. A hydraulic motor, driven by the pump previously used for the mid-upper turret was fitted to spin the bomb. Lamps were fitted in the bomb bay and nose for the simple height measurement system which enabled the accurate control of low-flying altitude at night. The mid-upper turret was removed to save weight and the gunner moved to the front turret to relieve the bomb aimer from having to man the front guns so that he could assist with map reading.

Lancaster ASR.III/ASR.3
B III modified for air-sea rescue, with three dipole ventral antennas fitted aft of the radome and carrying an airborne lifeboat in an adapted bomb bay. The armament was often removed and the mid-upper turret faired-over, especially in postwar use. Observation windows were added to both sides of the rear fuselage, a port window just forward of the tailplane and a starboard window into the rear access door. A number of ASR 3 conversions were fitted with Lincoln-style rudders.

Lancaster GR.3/MR.3
B.III modified for maritime reconnaissance.

Lancaster B.IV
The B.IV featured an increased wingspan and lengthened fuselage and new Boulton Paul F turret (two X 0.5in Browning machine guns) with framed "bay window" nose glazing. The prototypes (PW925, PW929 and PW932) were powered by two-stage Merlin 85s inboard and later, Merlin 68s on the outboard mounts. Because of the major redesign, the aircraft was quickly renamed Lincoln B 1.

Lancaster B.V
Increased wingspan and lengthened fuselage, two-stage Merlin 85s. Renamed Lincoln B 2

Lancaster B.VI
Nine aircraft converted from B.IIIs. Fitted with Merlin 85/87 which had two-stage superchargers, giving much improved high altitude performance. The B VI could achieve a maximum speed of 313 mph (505 km/h) at 18,200 ft (5,550 m) at 65,000 lb (29,500 kg) take off weight and a service ceiling of 28,500 ft (8,690 m) at the same weight. Climb to 28,000 ft (8,500 m) at 65,000 lb (29,500 kg) take off weight was accomplished in 44.8 minutes with a maximum climb rate of 1,080 ft/min (5.5 m/s) at 1,000 ft (305 m). A Lancaster B VI was dived to a maximum indicated speed of 350 mph (565 km/h), or Mach 0.72 at 25,000 ft (7,620 m) in June 1944. The Merlin 85/87 series engines were fitted with annular cowlings similar to the Avro Lincoln and three bladed paddle-type propellers were fitted. These aircraft were only used by Pathfinder units; by No. 7 Squadron RAF, No. 83 Squadron RAF, No. 405 Squadron RCAF and by No. 635 Squadron RAF. Often used as a "Master Bomber" the B VI's were allocated to RAF Bomber Command apart from two that were retained by Rolls-Royce for installation and flight testing. Their dorsal and nose turrets were removed and faired-over. The more powerful engines proved troublesome in service and were disliked by ground maintenance staff for their rough running and propensity to 'surge and hunt', making synchronisation impossible. This was caused by variations in the fuel/air mixture and over time would damage the engine. The B VI was withdrawn from operational service in November 1944 and surviving aircraft were used by Rolls-Royce, the Royal Aircraft Establishment and the Bomb Ballistics Unit (BBU) for various testing and experimental duties.

Lancaster B.VII
The B.VII was the final production version of the Lancaster. The Martin 250CE mid-upper turret was moved slightly further forward than on previous Marks and the Nash & Thomson FN-82 tail turret with twin 0.50 in (12.7 mm) Browning machine guns replaced the FN.20 turret with four Browning .303 Mark IIs. The Martin turret carried two 0.5 inch Browning Mark II machine guns which packed much more punch than the .303s of the older turret. However, these Martin turrets arrived too late for inclusion in the first 50 aircraft built by Austin and these were therefore referred to as Mark VII (Interim). Another 180 true Mark VIIs were built at Longbridge. Two sub-variants of the VII existed, the "Far East" (B VII FE) for use in tropical climates and the B VII "Western Union", which went to France.

Lancaster B.X
The B.X was a Canadian-built B.III with Canadian- and US-made instruments and electrics. On later batches the heavier Martin 250CE was substituted for the Nash & Thomson FN-50 mid-upper turret, mounted further forward to maintain centre of gravity balance. Canada was a long term operator of the Lancaster, using modified aircraft after the war for maritime patrol, search and rescue and photo-reconnaissance until 1964. The last flight by the RCAF was by F/L Lynn Garrison in KB-976, on 4 July 1964 at the Calgary International Air Show. During the Second World War, Canada's Victory Aircraft (what later became Avro Canada) was responsible for the development of the Lancastrian, which was duly designated the XPP for Mark 10 Passenger Plane. Six were built for Trans Canada Airlines. Postwar the RCAF modified the B X (as the Lancaster Mk 10) to fill a variety of roles, with specific designations for each role.

These included:
  10AR: Area Reconnaissance Electronic Warfare aircraft with lengthened nose.
  10BR: Bomber Reconnaissance
  10DC: Drone controller with Ryan Firebee drones – 2 modified.
  10MR (later 10MP): Maritime Reconnaissance or Maritime Patrol Anti-submarine warfare aircraft
  10N: Navigational trainer
  10O: Orenda jet engine testbed for the engine used in the Avro CF-100.
  10P: Photo reconnaissance mapping duties
  10SR: Air-sea Search and Rescue aircraft – 8 modified.
  10S and 10U: Standard aircraft and Unmodified aircraft held in storage for future use or for transfer to museums.

Lancaster B.XV
As per Lancaster B.IV/Lincoln B.1 but built in Canada and renamed Avro Lincoln XV. One example built before order cancelled when war ended.