A RAF Vickers Wellington. National Archives of Canada, PA-144537.

The success of a bombing mission rests on three factors: the capacity to enter enemy territory while withstanding fire from anti-aircraft defences, the accuracy of navigation and target identification, and the quantity and efficiency of the bombs dropped on the target.

In 1940-1941, none of the medium bombers (twin-engine Armstrongs, Whitworth Whitleys and Handley Page Hampdens) flew fast enough, manoeuvred well enough, or was sufficiently armed to survive a bombing mission over Germany. The Vickers Wellington, on the other hand, proved rather successful and was soon viewed as the best aircraft Bomber Command could use on strategic bombing missions against the enemy. It could carry 2,900 pounds (1,315 kg) of bombs; its armament, however, was not adequate to deal with German fighter aircraft and it could not fly high enough to escape Flak.

Canadian-made Lancasters X of No 419 Squadron on the Middleton St. George air base, May 1st, 1944. The plane in the foreground marked KB 711 was shot down later that same evening during a raid over St-Ghislain. National Defence Image Library, PL 29474.

The RAF had to use heavy bombers, rapid four-engine airplanes that could carry a significant load and had enough firepower to defend themselves against Luftwaffe fighters. The British aeronautical industry produced three such heavy bombers: Short Stirlings, Handley Page Halifax and Avro Lancasters, but the quantities produced did not meet RAF requirements. In 1943, the Stirling was withdrawn from bombing mission over Germany, its flight ceiling being too low. The Halifax and the Lancaster remained for the whole duration of the war as Bomber Command’s all-around heavy-duty aircraft.

The Avro Lancaster, viewed as the best WWII heavy bomber, could carry up to 14,000 pounds (6,350 kg) of bombs. A modified version could take on the heaviest bomb ever produced for Bomber Command, the 22,000-pound (10,000-kg) “Grand Slam”. Its seven-member crew included a pilot, a flight engineer, a navigator, a wireless operator, a bomb-aimer/front gunner, a mid-upper gunner, and a rear gunner. The Lancaster Mark X was built in the Canadian shops of Victory Aircraft in Toronto, with deliveries starting in 1944; by May 1945, six Canadian squadrons were equipped with Mark X.

Bombs

Different types of bombs used by Bomber Command: the smallest weighing 40 pounds (18 kg), the biggest, the “Grand Slam” tipping the scale at 22,000 pounds (10,000 kg). Markings refer to medium casing (MC) or heavy casing (HC). Department of National defence / National Archives of Canada, PA-213867.

Bombs, like airplanes, needed many improvements. The first bombs dropped in 1941 contained too much metal and not enough explosives, therefore inflicting little damage to the targets. The quantity of explosive matter was increased, with Amatol or TNT used in the high explosive (HE) bombs. Bomber Command also developed larger bombs to be used depending on the nature of the target: general purpose bombs weighed 250 or 500 pounds (113 or 225 kg), while “blockbusters” weighed between 2,000 pounds (907 kg) and 12,000 pounds (5,443 kg). The “Grand Slam”, a deep-penetration bomb used in the last months of the war weighed as much as 22,000 pounds (10,000 kg). There were bombs that could be set to explode some time after contact with the target, once they have already penetrated a structure or the ground. Others may explode hours after the impact in order to hamper the work of rescue and clean-up crews.

Incendiary bombs were also used; they were usually made of a cylinder filled with hundreds of small 4-pound (1.8-kg) magnesium charges, or of fewer, heavier, 30-pound (13,6 kg) charges. The cylinder opened at an altitude of 600 metres so the incendiary charges would spread before reaching the target. Combining explosive and incendiary bombs caused maximum damage: explosive bombs blasting walls and windows open to help fire propagate as fast and as far as possible.

Radar and Navigation

No 432 Squadron armourers loading general purpose 1,000-pound (454-kg) bombs in the bomb bay of a Halifax, East Moor, February 2nd, 1945. Gérard Pelland’s album; by kind permission of the Pelland family. F/O Gus Utah, navigator on a 427 Squadron bomber; Ruthless Robert, the crew’s mascot keeps him company. National Defence Image Library, PL 28520.

Night navigation was the most difficult issue: with the techniques available in 1940 – using ground features, by the stars, or by estimating time of arrival on the basis of the aircraft and wind speed – only a seasoned navigator could hope locating his target with some accuracy. Aiming in the dark and through the clouds was even more difficult when the bomber had to find its way through Flak and blinding spotlights. Scientists worked frantically on developing navigation systems that could help bombers better identify their position.

In early 1942, bombers were supplied with a Gee receiver, a system that picked up a synchronized signal from three stations located in Great Britain. By measuring the time difference between individual signals, the navigator could determine the distance from each of the stations and triangulate the aircraft’s position. The Oboe radar system was also introduced in 1942: it used radar signals from two ground stations, one keeping the aircraft along a course that passed over the target, the second signal indicating when the bombs should be dropped. In 1943, the RAF introduced the H2F radar, an airborne radar pointing towards the ground that provided a rough image of features such as rivers, lakes and cities. With those different systems, navigators and pilots could reach their target by night, provided naturally that the bomber could fly past German anti-aircraft defences. New systems were introduced in 1943 and 1944 to detect enemy aircraft, scramble their radars and saturate their communications.

Despite all this technical progress, identifying the target with precision remained a difficult task. A special force was created, the Pathfinders, tasked with locating and flagging targets with flare bombs known as “target indicators” (TI). Pathfinders would reach the target first and drop colour TIs that could easily be seen through smoke and flames. Bombers coming behind in waves dropped their bombs using the TIs as guides. All those measures helped Allied bombers greatly improve the accuracy of their operations.