Armament

Defensive

While eight .303 in (7.7 mm) machine guns were the most common Lancaster armament, twin .50 in (12.7 mm) turrets were later available in both the tail and dorsal positions. A Preston-Green mount was available for a .50 in (12.7 mm) mounted in a ventral blister, but this was mostly used in RCAF service. This blister was later the location for the H2S radar. A Nash & Thomson FN-64 periscope-sighted twin .303 in (7.7 mm) ventral turret was also available but rarely fitted as it was hard to sight. (Similar problems afflicted the ventral turret in the North American B-25C and other bombers). Some unofficial mounts for .50 in (12.7 mm) machine guns or even 20 mm cannon were made, firing through ventral holes of various designs.

Bombs

An important feature of the Lancaster was its extensive bomb bay, at 33 ft (10.05 m) long. Initially, the heaviest bombs carried were 4,000 lb (1,820 kg) "Cookies". Bulged doors were added to allow the aircraft to carry 8,000 lb (3,600 kg) and later 12,000 lb (5,450 kg) "Cookies". Towards the end of the war, attacking special and hardened targets, the B I Specials could carry the 21 ft (6.4 m) long 12,000 lb (5,450 kg) "Tallboy" or 25.5 ft (7.77 m) long 22,000 lb (9,980 kg) "Grand Slam" "earthquake" bombs: the Lancaster was able to deliver the heaviest bombs made. To carry the "Grand Slam" extensive modifications to the aircraft were required which led to them being redesignated as B I (Specials). The modifications included removal of the mid-upper turret, two guns from the rear turret, removal of all of the cockpit armour plating and installation of Rolls-Royce Merlin Mk 24 Engines which had better take-off performance. The bomb-bay doors were removed and the rear end of the bomb bay cut away to clear the tail of the bomb. Later the nose turret was also removed to further improve performance.

Bombsights used on Lancasters included:

Mark IX Course-Setting Bombsight (CSBS).

This was an early preset vector bombsight that involved squinting through wires that had to be manually set based on aircraft speed, altitude and bombload. This sight lacked tactical flexibility as it had to be manually adjusted if any of the parameters changed and was soon phased out in favour of the bombsights below.

Mark XIV bombsight

A vector bombsight where the bomb aimer input various details of the bombload, target altitude and wind direction, and the analogue computer then continuously calculated the trajectory of the bombs and projected an inverted sword shape onto a sighting glass on the sighting head. Assuming the sight was set correctly, when the target was in the cross hairs of the sword shape, the bomb aimer would be able to accurately release the bombs.

T1 bombsight

A Mark XIV bombsight modified for mass production and produced in the USA. Some of the pneumatic gyro drives on the Mk XIV sight were replaced with electronic gyros and other minor modifications were made.

Stabilizing Automatic Bomb Sight

Also known as "SABS", this was an advanced bombsight mainly used by 617 Squadron for precision raids. Like the American Norden bombsight it was a tachometric sight.

Radio, radar and countermeasures equipment

The Lancaster had a very advanced communications system for its time. Most British-built Lancasters were fitted with the R1155 receiver and T1154 transmitter, whereas the Canadian built aircraft and those built for service in the Far East had American radios. These provided radio direction-finding, as well as voice and Morse capabilities.

H2S

Ground-looking navigation radar system - eventually, it could be homed in on by the German night fighters' NAXOS receiver and had to be used with discretion.

Fishpond

An add-on to H2S that provided additional (aerial) coverage of the underside of the aircraft to display attacking fighters on an auxiliary screen in the radio operator's position.

Monica

A rearward-looking radar to warn of night fighter approaches. However, it could not distinguish between attacking enemy fighters and nearby friendly bombers and served as a homing beacon for suitably-equipped German night fighters. Once this was realised, it was removed altogether.

GEE

A receiver for a navigation system of synchronized pulses transmitted from the UK - aircraft calculated their position from the time delay between pulses. The range of GEE was 3-400 mi (483-644 km).

Boozer (radar detector)

A system of lights mounted on the aircraft's instrument panel that lit up when the aircraft was being tracked by Würzburg ground radar and Lichtenstein airborne radar. In practice it was found to be more disconcerting than useful, as the lights were often triggered by false alerts in the radar-signal-infested skies over Germany.

Oboe

A very accurate navigation system consisting of a receiver/transponder for two radar stations transmitting from widely separated locations in Southern England which together determined the range and the bearing on the range. The system could only handle one aircraft at a time, and was fitted to a Pathfinder aircraft, usually a fast and manoeuvrable Mosquito rather than a heavy Lancaster, which marked the target for the main force.

GEE-H

Similar to Oboe but with the transponder on the ground allowing more aircraft to use the system simultaneously. GEE-H aircraft were usually marked with two horizontal yellow stripes on the fins.

Village Inn

A radar-aimed gun turret fitted to some Lancasters in 1944.

Airborne Cigar (ABC)

This was only fitted to the Lancasters of 101 Squadron. It was three aerials, two sticking out of the top of the fuselage and one under the bomb aimer's position. These were used to jam radio to German night fighters. Fitted from about mid-1943, they remained until the end of the war.