An important feature of the Lancaster was its unobstructed, 33 ft (10.05 m) long, bomb bay. At first, the heaviest bomb carried was the 4,000 lb (1,820 kg) high capacity HC "Cookie".[18] Bulged doors were added to 30% of B Is to allow the aircraft to carry 8,000 lb (3,600 kg) and later 12,000 lb (5,450 kg) "Cookies". The Lancaster also carried a variety of smaller weapons, including the Small Bomb Container (SBC) which held 236 4 lb or 24 30 lb incendiary and explosive incendiary bomblets; 500 lb and 1,000 lb General Purpose High Explosive (GP/HE) bombs (these came in a variety of designs); 1,850 lb parachute deployed magnetic or acoustic mines, or 2,000 lb armour piercing (AP) bombs; 250 lb Semi-Armour-Piercing (SAP) bombs, used up to 1942 against submarines; post 1942: 250 lb or 500 lb anti-submarine depth charges.
In 1943 617 Squadron was created to carry out Operation Chastise, the raid against the Ruhr dams. This unit was equipped with B.III (Specials), officially designated the "Type 464 (Provisioning)", modified to carry the 9,250 pound (4,196 kg) "Upkeep" bouncing bomb (which was referred to as a mine).[19] The bomb bay doors were removed and the ends of the bomb bay were covered with fairings. "Upkeep" was suspended on pivoted, vee-shaped struts which sprang apart when the bomb-release button was pressed. A drive belt and pulley to rotate the bomb at 500 rpm was mounted on the starboard strut and driven by a hydraulic motor housed in the forward fairing. The mid-upper turret was removed and a more bulbous bomb aimer's blister was fitted; this later becoming standard on all Lancasters, while the bombsight was replaced by a simple aiming device.[20] Two Aldis lights were fitted in the rear bomb bay fairing; the optimum height for dropping "Upkeep" was 60 ft and, when shone on the relatively smooth waters of the dam's reservoirs, the light beams converged into a single spot when the Lancaster was flying at the correct height.[21]
Towards the end of the war, attacking special and hardened targets, other variants of B I Specials were modified to 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: to carry the "Grand Slam" extensive modifications to the aircraft were required. The modifications included removal of the mid-upper turret and the removal of two guns from the rear turret; removal of the cockpit armour plating (the pilot's seatback) 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. The undercarriage was strengthened and stronger mainwheels, later used by the Avro Lincoln, were fitted.[4][22]
Specific bomb loads were standardized and given code names by Bomber Command:[23]
Codename
Type of raid or target
Bomb load
"Arson"
incendiary area bombing
14 SBC, each with 236 x 4 lb Incendiary and Explosive Incendiary bomblets.
"Abnormal"
factories, railway yards, dockyards
14 x 1,000 lb GP/HE bombs using both impact and long delay (up to 144 hours) fuses.
"Cookie"—or—"Plumduff"
Blast, demolition and fire
1 x 4,000 lb impact-fused HC bomb. 3 x 1,000 lb GP/HE bombs, and up to 6 SBCs with incendiary bomblets.
"Gardening"
Mining of ports, canals, rivers and seaways
6 x 1,850 lb parachute mines.
"No-Ball"
V-1 flying bomb launch sites
1 x 4,000 lb impact fused HC and up to 18 x 500 lb GP bombs, with both impact and delay fusing.
"Piece"
Docks, fortifications and ships
6 x 2,000 lb short-delay fused AP bombs, plus other GP/HE bombs based on local needs or availability.
"Plumduff-Plus"
Heavy industry
1 x 8,000 lb impact or barometric fused HC and up to 6 x 500 lbs impact or delay fused GP/HE bombs.
"Usual"
Blast and incendiary area bombing
1 x 4,000 lb impact-fused HC bomb, and 12 SBCs with incendiary bomblets.
no code name given
Medium-range low altitude tactical raids
6 x 1,000 lb short and long delay fused GP/HE bombs, additional 250 lb GP/HE bombs sometimes added.
no code name given
Submarines
(up to 1942): 5 x 250 lb short delay fuse SAP bombs for surfaced U-boats; (post-1942): 6 x 500 lb and 3 x 250 lb anti-submarine depth charge bombs.
Special purpose weapons and codenames
Type of target
Weapon
"Grand Slam"
Underground or armoured facilities
1 x 22,000 lb short-delay fused "Grand Slam" bomb.
"Tallboy"
Very strong or durable structures (e.g.: submarine pens); battleship Tirpitz
1 x 12,000 lb short-delay fused "Tallboy" bomb.
"Upkeep"
Dams
1 x 9,250 lb, hydrostatic-fused "Upkeep" mine.
