Other changes also affected bomber capabilities. The Germans embraced dive-bombing, and all their bombers had to be able to dive-bomb. The necessary structural changes greatly added to the bombers' weight and decreased bomb loads. The flying weight of the Ju-88, for example, went from 6 to 12 tons, sharply reducing both its speed and bomb-carrying capacity.
Defensive armament of the majority of bombers in service at the start of the war was inadequate in terms of the number and caliber of weapons and/or their field of fire. This situation came about partly because of the assumption that interceptions at 300-plus mph were difficult and would therefore be rare. The early B-17Cs, for example, were quite vulnerable because their few defensive weapons had several blind spots and were single manually aimed weapons. Later B-17Es had much better defensive armament deployed as multiple weapons in power turrets, making them much more difficult to shoot down. An alternative tactic was to dispense with all defensive weapons and rely on speed and performance to evade the defenses. The De Havilland Mosquito, which carried out many pinpoint attacks from 1942 onward, epitomized this approach.
The following text describes the most significant bombers employed by both sides during World War II.
The Heinkel He-111 entered service in 1935, and the B model served with distinction in the Spanish Civil War, where it was fast enough to fly unescorted. Nearly 1,000 He-111s were in service at the start of the war; they formed a significant part of the Luftwaffe's medium bomber strength early in the conflict, although they were roughly handled during the Battle of Britain in spite of carrying nearly 600 lb of armor. Later versions had better defensive armament and were used in various roles, including torpedo bombing. Approximately 7,450 He-111s were built before production ended in 1944.The prototype Junkers Ju-87 Stuka dive-bomber flew in 1935, entering service with the Luftwaffe in spring 1937. Examples sent to Spain with the Kondor Legion in 1938 were able to demonstrate highly accurate bombing under conditions of air superiority. Stukas were highly effective in the invasions of Poland in 1939 and France in 1940. During the Battle of Britain, they suffered such heavy losses from opposing British fighters that they were withdrawn from operations partway through the campaign. However, they continued to serve in the Mediterranean Theater and on the Eastern Front against the Soviet Union in dive-bombing and close ground-support roles. A total of 5,709 Ju-87s of all versions were built.
The Junkers Ju-88, one of the most effective and adaptable German aircraft of the war, entered Luftwaffe service in September 1939. The Ju-88 had good performance for a bomber, particularly the later versions, which were used as night fighters. Specialized variants were also produced for dive-bombing, antishipping, reconnaissance, and training. Ju-88C fighter variants were used in daylight during the Battle of Britain, but they were unable to cope with attacks by modern British single-engine fighters. A total of 14,980 Ju-88s were built, 10,774 of which were bomber variants.
The principal Italian bomber, and one of the most capable Italian aircraft of the war, was the trimotor Savoia-Marchetti SM.79 Sparviero (Sparrow). The Italians used it as a bomber, torpedo-bomber, and reconnaissance aircraft. Originally designed by Alessando Marchetti as a high-speed, eight-passenger transport, it had retractable landing gear. The SM.79 entered service in 1936 and first saw service in the Spanish Civil War. A total of 1,217 were produced during World War II. Reconverted to military transports after the war, Sparvieros served with the Italian air force until 1952.The CANT Z.1007 Allcione (Kingfisher) was Italy's second-most-important bomber of the war. Entering production in 1939, it was both a medium conventional bomber and a torpedo-bomber. It was of largely wooden construction with weak defensive armament. It appeared both in single- and twin-rudder configurations without differing designations and often in the same squadron. The CANT Z.1007 was widely used all over the Mediterranean Theater. Of good design and easy to fly, it was nonetheless poorly defended and suffered heavy losses from Royal Air Force (RAF) fighters. CANT Z.1007s continued in service until the end of the war on both sides after the Italian surrender of 1943. A total of 560 were built.
The Italians had only one 4-engine bomber, the Piaggio P.108. Designed by Giovanni Casiraghi, it entered service in May 1941 and was only intermittently used. It had a crew of 6, a maximum speed of 261 mph, and a range of 2,190 mi. Armed with 8 machine guns, it could carry 7,700 lb of bombs. Only 33 were produced, however, 8 of which went to the Germans for use as transports.
The Mitsubishi Ki-21 medium bomber ("Sally" in Allied designation) was the winner of a 1936 bomber design competition run by the Japanese army air force. It entered service in 1937 as the Ki-21-Ia and was replaced shortly afterward by the Ki-21-Ic, which had additional armament and defensive armor as a result of combat experience in China. The Ki-21 was the standard Japanese air force bomber at the end of 1941 and was encountered throughout the Pacific and the Far East. When production ended in 1944, 2,064 had been built by Mitsubishi and Nakajima, as well as about 500 transport versions by Mitsubishi.The Mitsubishi G4M medium bomber ("Betty") entered service with the Japanese army early in 1941 and was involved in pre–World War II operations in China. It was designed in great secrecy during 1938–1939 to have the maximum possible range at the expense of protection for the crew and vital components, and it was mainly used in the bomber and torpedo-bomber roles. G4M1s were mainly responsible for sinking the British battleship Prince of Wales and battle cruiser Repulse off Malaya in December 1941. The G4M had an extraordinary range, but more than 1,100 gallons of fuel in unprotected tanks made the aircraft extremely vulnerable to enemy fire. The G4M2 appeared in 1943 and was the major production model, with more-powerful engines and even more fuel. Losses of the aircraft continued to be very heavy, and Mitsubishi finally introduced the G4M3 model late in 1943 with a redesigned wing and protected fuel tanks. A total of 2,479 aircraft in the G4M series were built.
The Bristol Blenheim was developed from the private-venture Bristol 142, and the short-nosed Mk 1 entered service as a light bomber in March 1937, although some were completed as fighters. The Blenheim was an effective bomber, but lacking adequate defensive armament and armor, it was vulnerable to fighter attack. The most numerous versions were the long-nosed Mk IV and V, but their performance suffered from significant weight growth, the Mark V in particular suffering heavy losses. The Blenheim nevertheless filled an important capability gap in time of need, and it was exported to Finland, Romania, Turkey, and Yugoslavia. A total of 5,213 Blenheims of all versions were built.The Vickers Wellington entered service with the RAF late in 1938 and (with the Whitley and Hampden) bore the brunt of the RAF bomber offensive for the first two years of the war. Its light but strong geodetic structure enabled it to carry a respectable bomb load, and it could withstand a significant amount of battle damage. The Wellington was one of the first monoplane bombers to be fitted with power turrets, but (in common with all early World War II bombers) it was vulnerable to fighter attack when flown unescorted in daylight. The Wellington was mainly employed as a medium bomber, although some were used for maritime reconnaissance, torpedo-bombing, minelaying, and transport duties. Wellingtons were in production throughout the war, 11,461 being built up to October 1945.
The Handley Page Hampden entered RAF service late in 1938. Of imaginative design, it delivered a reasonable performance on only average engine power, but the cramped fuselage caused crew fatigue, and the defensive field of fire was very limited. Hampdens were used as medium bombers and minelayers until late 1942, and they served as torpedo-bombers and maritime reconnaissance aircraft until the latter part of 1943. A total of 1,430 Hampdens and variants were built.
The Short Stirling, the first of the RAF's four-engine "heavies" to see combat, entered service in late 1940. It was built to specification B.12/36, which unfortunately specified that the wingspan should be less than 100 ft to fit in a standard hangar; this compromised the aircraft's altitude capability to the extent that attacks on Italy required British pilots to fly through the Alps rather than over them. However, the Stirling was outstandingly maneuverable for such a large aircraft. It was used as a bomber, minelayer, glider tug/transport, and (with 100 Group) an electronic countermeasures aircraft. A total of 2,381 Stirlings were built.
The Handley Page Halifax I entered service early in 1941 and was found to be a good bomber, but it lacked adequate defensive armament. The Halifax B.II had a dorsal gun turret but suffered from weight growth and a tendency to spin when fully loaded. Later B.IIs underwent a weight- and drag-reduction program and had larger fins fitted to correct these faults. The B.III version was the most numerous, using more powerful Bristol Hercules engines in place of the Merlins. Although the Halifax's main role was as a bomber, it was also employed as a transport, glider tug, and maritime reconnaissance aircraft. A total of 6,176 Halifaxes were built.
The Avro Lancaster was a successful development of the Rolls-Royce Vulture-powered Manchester, entering operational service with the RAF in early 1942. The Lancaster remained in service until the end of the war and rapidly became the primary strategic bomber for the RAF. It lost fewer aircraft per ton of bombs dropped than either the Halifax or Stirling. The Lancaster had a large bomb bay and was designed to take 4,000 lb bombs; successive modifications enabled it to carry 8,000 lb and 12,000 lb weapons, and the B.I (special) carried a single 22,000 lb "Grand Slam" armor-piercing bomb. The Lancaster participated in several special operations, including the Dambusters raid in May 1943, when specially adapted Lancasters of 617 Squadron attacked dams in the Rhine valley using a skipping bomb designed by Barnes Wallis. A total of 7,366 Lancasters were built.
The De Havilland Mosquito was constructed largely from a plywood/balsa sandwich and was designed to be fast enough to outrun enemy fighters. It had excellent handling characteristics. It began operations with the RAF in the bomber role early in 1942 and quickly demonstrated that it could carry out extremely accurate attacks, including the daring low-level attack on the Gestapo headquarters in Oslo, Norway, in late 1942. Mosquitoes originally equipped the RAF's pathfinder force, and they were able to roam across Germany largely unmolested. Operationally, the Mosquito had by far the lowest loss rate of any aircraft in Bomber Command (about 0.6 percent), as its speed enabled it to avoid most interception and its structure tended to absorb cannon hits. A total of 6,439 Mosquitoes of all marks were built.
The Ilyushin Il-4 was the most widely used Soviet medium bomber of the war. Initially designed as the DB-3 in 1935, it entered service in that form in 1938. The updated DB-3F was redesignated Il-4 in 1940, and many examples were built. Following the Soviet entry into the war, a force of Soviet Navy Il-4s carried out the first Soviet attack on Berlin in August 1941. As a result of shortages of strategic materials, parts of the airframe including the outer wing panels were redesigned to use wood instead of metal. The Il-4 was a maneuverable aircraft in spite of its size, and approximately 5,000 were built up to 1944.The Petlyakov Pe-2 entered service early in 1941. It was originally designed as a fighter and therefore had unusually responsive controls for a bomber. It turned out to be one of the most versatile aircraft produced by the USSR in the war, being used as a heavy fighter, light bomber, dive-bomber, ground-attack, and reconnaissance aircraft. More than 11,000 Pe-2s were built.
The Ilyushin Il-2 Shturmovik was probably one of the most effective ground-attack aircraft of World War II, entering service on the Soviet Front in mid-1941. Initial versions were single-seaters, but the higher-performance Il-2m3 introduced in mid-1942 had a gunner and was highly effective in aerial combat at low altitude, even against single-seat German fighters. Later versions of the Il-2m3 had a more powerful engine and a 37 mm cannon against German Panther and Tiger tanks. The Shturmovik was remarkably tough; about 15 percent of its empty weight was armor plate that protected the engine, fuel systems, and crew, and it had few weak points. Approximately 35,000 Shturmoviks were built.
The Boeing B-17 Flying Fortress was designed in 1934 and sold to Congress as a U.S. Army Air Corps requirement for an offshore antishipping bomber. The B-17B entered service late in 1939; it was fast and had a high operational ceiling, but the initial versions were not particularly capable. The B-17E, which entered service early in 1942, had much-improved defensive armament, including a tail gun turret, and the B-17G (late 1943) introduced an additional chin turret, which was later fitted to some F models. The B-17 E, F, and G models formed the mainstay of the U.S. heavy day-bomber force in Europe and remained in service until the end of the war. There were 8,685 B-17s built.The Consolidated B-24 Liberator heavy bomber was designed with a high aspect-ratio wing that, together with its Davis high-lift airfoil, gave very good range/payload performance. The first Liberators entered service with RAF Coastal Command in mid-1941, and the type went on to serve with the U.S. Army Air Forces (USAAF) and U.S. Navy. USAAF B-24s conducted the ill-fated raid on the Ploesti oil field on 1 August 1943. The Liberator developed a reputation for fragility in the European Theater and was prone to catch fire when hit, but its long range made it the preeminent strategic bomber in the Pacific Theater. The B-24 was employed as a reconnaissance, antisubmarine, and transport aircraft as well as in its primary strategic bombing role, and it was produced in greater quantities than any other American aircraft, 18,188 being built up to May 1945.
The Douglas Aircraft Company built the A-20 attack bomber as a private venture, albeit with the help of U.S. Army Air Corps technicians at the specification stage. It entered service early in 1940 with the French Armée de l'Air, outstanding orders being transferred to the RAF when France capitulated to the Germans. The A-20 (designated Boston or Havoc, depending on the role) was an excellent airplane. Fast, docile, and pleasant to fly, it had a commendably low loss rate. It was very adaptable and was produced in both solid-nose and transparent-nose versions. Used in many roles including low-level attack, strafing, torpedo-bombing, reconnaissance, and night fighting, it remained in frontline service until the end of hostilities. A total of 7,385 variants were built.
North American was awarded a contract to build the B-25 Mitchell without the usual prototypes, relying instead on experience with the NA-40 design and feedback from the Army Air Corps. Self-sealing fuel tanks and armor protection were incorporated on the production line following combat reports from Europe. The Mitchell had good handling characteristics and was probably the best all-around medium bomber of the war. The B-25 achieved lasting fame when 16 of them attacked Tokyo in April 1942, flying from the carrier Hornet. The Mitchell was adapted to multiple missions including ground strafing, torpedo-bombing, antisubmarine work, and reconnaissance, mounting a variety of main armament including up to 18 0.5-inch machine guns in the B-25J and a 75 mm cannon in the B-25H. Mitchells were used by most Allied air forces, and approximately 11,000 were built.
The Boeing B-29 Superfortress, the heaviest bomber of the war, evolved from a 1940 Army Air Corps requirement for a "hemisphere defense weapon." The resulting XB-29, which first flew late in 1942, had several innovative design features including a pressurized fuselage and remote-controlled gun turrets. The B-29 entered service in the first half of 1944 and mounted increasingly heavy attacks against the Japanese mainland from bases in the Mariana Islands. Operationally, the B-29 was successful largely as a result of its speed and altitude capabilities. B-29s forced the Japanese surrender following attacks with atomic bombs on Hiroshima and Nagasaki during August 1945. A total of 3,970 were built.
The Douglas A-26 Invader was a worthy successor to the Douglas A-20 Havoc. It entered service late in 1944. The A-26B had a solid attack nose carrying six .50 caliber machine guns, and the A-26C had a more conventional transparent nose for a bombardier. The A-26 was fast and well armed, and it had a very low loss rate (about 0.6 percent), even allowing for low enemy fighter activity toward the end of the war. A total of 2,446 Invaders were built, and they continued to serve for many years after the war.
The Martin B-26 Marauder entered service early in 1942 and initially gained a reputation as a difficult aircraft to fly, partly because of its weight and high landing and takeoff speeds. Certainly it required skill and practice to master. In later models (B-26F onward), the wing incidence was increased to reduce the landing and takeoff speeds. The B-26 could absorb a lot of damage and was an effective bomber; its final combat loss rate was less than 1 percent. A total of 5,157 Marauders were built. Andy Blackburn
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