The Second World War was, among other things, a war fought from the air. Bombers attacked factories, railways, ports, airfields, ships, troop concentrations, bridges, cities, and oil refineries. They supported armies in the field and attempted to destroy the industrial capacity that allowed the enemy to continue fighting.

The Allies eventually deployed an extraordinary variety of bombers. Britain developed the famous Lancaster, Halifax, and Stirling; the United States produced the B-17 Flying Fortress, B-24 Liberator, B-25 Mitchell, and B-29 Superfortress; the Soviet Union relied heavily on the Il-4, Pe-2, and Tu-2; Canada, Australia, New Zealand, South Africa, and other Allied nations also operated or produced important types.

The story of these aircraft is also the story of changing bombing doctrine. In 1939, many air forces still believed that bombers could operate independently and destroy an enemy’s industrial system. By 1945, experience had demonstrated that successful bombing required fighter escort, navigation systems, radar, intelligence, weather forecasting, specialized aircraft, and enormous logistical organizations.

Most importantly, the definition of a “bomber” changed during the war. A heavy four-engine bomber such as the Lancaster was designed for long-range strategic bombing, while aircraft such as the B-25 Mitchell or A-20 Havoc were intended primarily for tactical operations. Dive bombers and fighter-bombers filled yet another role.

This article focuses on Allied bomber aircraft, organized by nation, while distinguishing strategic, medium, light, tactical, and specialized bombers.

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Britain: The Heart of the Allied Bomber Offensive

Britain entered the war with perhaps the most developed strategic bombing doctrine among the Allied nations.

The Royal Air Force had created Bomber Command as an independent organization in 1936. British planners believed that a large force of long-range bombers could strike Germany’s industrial centers and undermine its ability to wage war.

The reality proved considerably more complicated.

The RAF initially lacked the navigational technology, accuracy, and fighter protection necessary for daylight strategic bombing. Consequently, Britain increasingly turned toward night bombing.

This produced a succession of increasingly capable heavy bombers.

Armstrong Whitworth Whitley

The Armstrong Whitworth Whitley was one of the RAF’s principal bombers at the beginning of the war.

It was already becoming obsolete by 1939, but it performed an important role during the early years of the conflict.

The Whitley participated in some of the RAF’s first bombing operations against Germany and later became particularly useful for:

• Training
• Transport
• Paratroop operations
• Special Operations Executive missions
• Maritime patrol

Its significance lies partly in demonstrating the rapid pace of bomber development during the war.

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Vickers Wellington

The Vickers Wellington was one of Britain’s most important early-war bombers.

Its geodetic construction gave it considerable strength, and it could absorb substantial battle damage.

The Wellington was a twin-engine medium bomber with a relatively modest bomb load compared with later heavy bombers.

Nevertheless, it remained in service throughout much of the war.

It was used for:

• Strategic bombing
• Anti-submarine warfare
• Maritime patrol
• Mine-laying
• Training

The Wellington became particularly important in the Mediterranean and Coastal Command.

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Handley Page Hampden

The Handley Page Hampden was another important RAF bomber at the beginning of the war.

Fast and relatively maneuverable for a bomber, the Hampden was used extensively during the early bombing campaign.

It also participated in torpedo-bombing and anti-shipping operations.

The Hampden was eventually withdrawn from front-line bombing because newer aircraft offered much greater capabilities.

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The RAF’s Heavy Bombers

Britain’s bomber strategy increasingly shifted toward four-engine heavy bombers capable of carrying large bomb loads deep into Germany.

Three aircraft became especially important.

Short Stirling

The Short Stirling was Britain’s first four-engine heavy bomber.

It entered service in 1941.

The Stirling could carry a substantial bomb load and played an important role during the development of the RAF’s heavy bomber force.

It was nevertheless limited by its relatively low operational ceiling and was gradually replaced by the Lancaster and Halifax.

The Stirling continued to serve in:

• Bomber operations
• Glider towing
• Transport
• Special operations

Its contribution was therefore considerably broader than its bombing career.

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Handley Page Halifax

The Handley Page Halifax became one of Britain’s principal heavy bombers.

It entered operational service in 1941 and eventually flew more than 80,000 operational sorties.

The Halifax was continuously improved during the war.

Different versions received more powerful engines, improved defensive armament, increased bomb capacity, and better equipment.

The Halifax served alongside the Lancaster as one of the principal weapons of RAF Bomber Command.

It was also used by RAF Coastal Command and for transport and special operations.

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Avro Lancaster

The most famous British bomber of the war was the Avro Lancaster.

Entering service in 1942, the Lancaster represented a major advance over the RAF’s earlier bombers.

It could carry an enormous bomb load and had sufficient range to reach targets throughout Germany.

Its enormous internal bomb bay was particularly important.

The Lancaster could carry:

• Conventional high-explosive bombs
• Incendiary bombs
• The 12,000-pound Tallboy
• The 22,000-pound Grand Slam

The latter weapons allowed Lancasters to attack heavily protected targets such as submarine pens, bridges, tunnels, and hardened structures.

The Lancaster became the principal instrument of the RAF’s strategic bombing campaign.

It also participated in famous operations including the destruction of the German battleship Tirpitz.

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British Medium and Light Bombers

Britain did not rely solely on heavy bombers.

Bristol Blenheim

The Bristol Blenheim was one of the RAF’s most important bombers during the early years of the war.

It was originally designed as a fast bomber, but advances in fighter technology quickly made it vulnerable.

Blenheims suffered heavy losses during daylight operations.

Nevertheless, the aircraft continued to serve in:

• Night bombing
• Reconnaissance
• Fighter operations
• Maritime patrol

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Fairey Battle

The Fairey Battle was a light bomber.

It performed poorly during the German invasion of France and Belgium in 1940.

The Battle was too slow and insufficiently armed to survive effectively against modern German fighters.

Its experience helped demonstrate that prewar concepts of the light bomber had become obsolete.

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Douglas Boston/A-20 Havoc

Britain operated the American Douglas Boston, known in American service as the A-20 Havoc.

The aircraft was particularly useful for tactical bombing and low-level attacks.

It served extensively in the Mediterranean and Northwest Europe.

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Mosquito

The de Havilland Mosquito was one of the most remarkable aircraft of the war.

Although often categorized as a light bomber, it was really a highly specialized multirole aircraft.

Its wooden construction made it relatively light, while its twin engines gave it excellent speed.

Mosquitos were used for:

• Precision bombing
• Pathfinder missions
• Reconnaissance
• Night fighter operations
• Intruder missions
• Special operations

Because it was so fast, the Mosquito could sometimes operate without heavy defensive armament.

It represented an entirely different solution to bomber survivability:

rather than absorb enemy fire, simply be too fast to catch.

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The United States: Mass Production and the Strategic Bombing Offensive

American bomber development followed a somewhat different path.

The United States Army Air Forces placed enormous emphasis on daylight precision bombing.

American doctrine argued that accurately bombing industrial targets could cripple an enemy’s ability to make war.

This required long-range bombers capable of carrying substantial bomb loads while defending themselves.

Initially, American planners believed that heavily armed bombers could defend themselves against enemy fighters.

The European war demonstrated the limitations of this assumption.

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Boeing B-17 Flying Fortress

The Boeing B-17 Flying Fortress became the symbol of American daylight strategic bombing.

It was designed around four principles:

• Long range
• High altitude
• Heavy bomb load
• Heavy defensive armament

The B-17’s multiple machine-gun positions were intended to provide overlapping fields of defensive fire.

American bomber crews initially believed that formations of B-17s could defend themselves.

They were wrong.

The unescorted daylight raids of 1943 resulted in catastrophic losses.

The introduction of long-range fighter escorts eventually transformed the situation.

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Consolidated B-24 Liberator

The B-24 Liberator was arguably even more important than the B-17 in terms of numbers.

It had greater range and could carry a substantial bomb load.

The Liberator’s distinctive high-wing design and twin tail made it easily recognizable.

B-24s operated in virtually every major theater.

They were particularly important in:

• The European strategic bombing campaign
• The Mediterranean
• The Pacific
• Anti-submarine warfare
• Maritime patrol

The B-24 was also built in enormous numbers.

More than 18,000 Liberators were produced.

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Boeing B-29 Superfortress

The B-29 Superfortress represented the culmination of American heavy bomber development during the war.

It was considerably more advanced than the B-17 or B-24.

The B-29 featured:

• Pressurized crew compartments
• Remote-controlled defensive turrets
• Powerful engines
• Long range
• Large bomb capacity
• Advanced fire-control systems

It was specifically designed for the war against Japan.

Operating from bases in the Pacific, B-29s conducted increasingly destructive bombing raids against Japanese cities.

They initially attempted high-altitude precision bombing.

Weather and jet streams made this difficult.

The strategy eventually shifted toward low-level nighttime incendiary raids.

The B-29 also carried the atomic bombs dropped on Hiroshima and Nagasaki in August 1945.

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American Medium Bombers

The United States also produced an enormous variety of medium and light bombers.

North American B-25 Mitchell

The B-25 Mitchell became one of America’s most famous medium bombers.

It gained international fame through the Doolittle Raid against Japan in April 1942.

The B-25 was versatile and could operate from land bases in Europe, North Africa, and the Pacific.

Some variants were heavily armed for low-level attacks.

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Martin B-26 Marauder

The Martin B-26 Marauder developed a reputation as a difficult aircraft to fly, particularly because of its relatively high landing speed.

But once crews became accustomed to it, the Marauder developed an excellent combat record.

It eventually achieved one of the lowest loss rates among American bombers operating in Europe.

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Douglas A-20 Havoc

The A-20 Havoc was primarily a light bomber and attack aircraft.

It was heavily used in Europe, North Africa, and the Pacific.

The Soviet Union also received large numbers through Lend-Lease.

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Douglas A-26 Invader

The A-26 Invader entered service late in the war.

It was fast and heavily armed and could perform bombing and ground-attack missions.

Although it saw limited service during the Second World War, it became a highly successful postwar attack aircraft.

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Soviet Bombers

The Soviet Union entered the war with a large but uneven bomber force.

Soviet bomber doctrine emphasized tactical and operational support of the Red Army as well as longer-range attacks.

The catastrophic German invasion of 1941 destroyed or captured enormous numbers of Soviet aircraft on the ground.

The Soviet Union nevertheless rebuilt its air force rapidly.

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Ilyushin Il-4

The Ilyushin Il-4 was the Soviet Union’s principal long-range bomber.

It was used to attack German targets at considerable range and also served as a torpedo bomber.

The Il-4 could operate over the Baltic and Black Seas and conduct long-range strikes against German targets.

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Petlyakov Pe-2

The Petlyakov Pe-2 was one of the most important Soviet tactical aircraft.

It was officially a dive bomber, but it evolved into a highly versatile light bomber.

The Pe-2 was fast, maneuverable, and capable of carrying bombs accurately.

It became one of the principal Soviet aircraft supporting ground operations.

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Tupolev Tu-2

The Tupolev Tu-2 entered service during the war and became one of the Soviet Union’s best medium bombers.

It combined:

• Speed
• Range
• Bomb capacity
• Defensive armament

Production initially faced difficulties, but the Tu-2 became increasingly important during the later stages of the war.

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The Soviet Assault Aircraft

It is worth noting that the Soviet Union’s most important “bomber” in terms of supporting the Red Army was not technically a bomber.

The Ilyushin Il-2 Shturmovik was an armored ground-attack aircraft.

It carried bombs, rockets, and cannon and was designed to attack:

• Tanks
• Artillery
• Troops
• Vehicles
• Fortifications

The Il-2 illustrates an important difference between Soviet and Anglo-American air doctrine.

The Soviets placed enormous emphasis on direct support of ground forces.

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Canada

Canada played an important role in Allied bomber production and operations.

Canadian factories produced enormous numbers of British and American-designed aircraft, while Canadian airmen served throughout Bomber Command.

Canada also operated aircraft such as:

• Avro Anson
• Bristol Bolingbroke
• Handley Page Hampden
• Vickers Wellington
• Avro Lancaster
• Bristol Beaufighter

The Lancaster became particularly important to the Royal Canadian Air Force, which operated numerous Lancaster squadrons in Europe.

The British Commonwealth Air Training Plan also made Canada a major training center for Allied aircrew.

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Australia

Australia developed its own bomber capability as well as producing British-designed aircraft.

The most important Australian bomber was the Bristol Beaufort.

The Australian-built Beaufort became a highly effective torpedo bomber and maritime strike aircraft in the Pacific.

Australia also operated:

• Beaufort
• Hudson
• Wellington
• Mitchell
• Lancaster
• Boston

The Beaufort played an important role in attacking Japanese shipping and supporting Allied operations in the Southwest Pacific.

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New Zealand and South Africa

New Zealand and South Africa did not develop large indigenous bomber industries, but their airmen served extensively in Commonwealth squadrons.

The Royal New Zealand Air Force operated aircraft including:

• Wellington
• Lancaster
• Mosquito
• Ventura
• Hudson

The South African Air Force operated aircraft including:

• Bristol Blenheim
• Maryland
• Boston
• Marauder
• Wellington
• Baltimore

These forces were particularly important in North Africa and the Mediterranean.

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Poland, France, Norway, and Other Allies

Other Allied nations also operated bomber aircraft, frequently within British or American formations.

The Polish Air Force, for example, operated Wellington and Halifax bombers within the RAF structure.

Norwegian, Czech, French, Dutch, Belgian, and other Allied personnel also served in RAF and Allied bomber units.

This was one of the distinctive features of Allied air power.

The bomber offensive was genuinely international.

A Bomber Command formation could contain British, Canadian, Australian, New Zealand, Polish, Czech, Norwegian, French, and other aircrew.

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How Bomber Strategy Changed During the War

The aircraft are fascinating, but the most important story is how bomber doctrine changed.

In 1939, different nations entered the war with very different theories about what bombers should accomplish.

By 1945, experience had forced almost everyone to reconsider those theories.

Phase One: The Bomber Offensive Begins

In 1939 and 1940, strategic bombing was still heavily influenced by ideas developed during the interwar period.

Many military theorists believed that bombing could bypass enemy armies and attack the economic foundations of war.

But early operations exposed major problems.

Bombers had difficulty:

• Finding targets
• Navigating at night
• Accurately dropping bombs
• Defending themselves against fighters
• Operating in poor weather

The result was that bombing accuracy was often dramatically worse than planners had expected.

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Phase Two: Night Bombing

Britain responded by increasingly emphasizing night bombing.

The theory was straightforward.

If bombers were difficult for enemy fighters to intercept at night, they could penetrate deep into Germany with lower losses.

The RAF developed increasingly sophisticated navigation systems.

These included:

• Gee
• Oboe
• H2S radar
• Pathfinder techniques

The Pathfinder Force marked targets for the main bomber force.

This was a major development.

Instead of sending hundreds of aircraft independently toward a target, the RAF increasingly developed coordinated bombing streams.

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Phase Three: American Daylight Precision Bombing

The United States pursued a different strategy.

American doctrine emphasized daylight precision bombing.

B-17s and B-24s were expected to attack specific industrial targets.

The Americans believed their Norden bombsights and high-altitude bombing techniques could provide considerable accuracy.

In practice, weather, smoke, enemy defenses, and other factors made precision bombing considerably more difficult.

And there was another problem:

German fighters.

The Americans initially lacked fighters capable of escorting bombers all the way to many deep targets in Germany.

The result was the disastrous series of daylight raids during 1943.

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Phase Four: The Long-Range Fighter Escort

The turning point came with the development and deployment of long-range Allied fighters.

The P-51 Mustang became particularly important.

With drop tanks, Mustangs could accompany bombers deep into Germany.

Now German fighters had to fight not only the bombers but also large formations of Allied fighters.

This fundamentally altered the strategic bombing campaign.

The bomber was no longer expected to defend itself alone.

Instead, the bomber became part of an integrated system involving: bombers + escort fighters + radar + intelligence + navigation + ground support.

This was one of the most important developments in air warfare.

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Phase Five: The Transportation and Oil Campaign

As Allied air superiority increased, bombing became increasingly systematic.

The Allies began concentrating heavily on targets that supported the German military machine.

These included:

• Railways
• Bridges
• Oil refineries
• Synthetic fuel plants
• Aircraft factories
• Ball-bearing plants
• Communications centers
• Airfields

The oil campaign of 1944 was particularly devastating.

Germany could still produce tanks and aircraft.

But without sufficient fuel, it increasingly struggled to operate them.

This demonstrated that strategic bombing did not necessarily have to destroy an entire city or factory.

Sometimes the most effective target was the system that allowed the enemy’s military forces to function.

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Phase Six: Tactical Bombing

Meanwhile, tactical aviation became increasingly important.

The closer Allied armies moved toward Germany, the more air power was integrated directly into ground operations.

Aircraft such as the:

• B-25
• A-20
• B-26
• A-26
• Mosquito
• Typhoon
• Il-2
• Pe-2

were used against troop concentrations, artillery, vehicles, bridges, railways, and other battlefield targets.

The distinction between “bomber” and “attack aircraft” increasingly blurred.

Air power became an integrated component of combined-arms warfare.

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The Pacific: A Different Bombing War

The Pacific War created different requirements.

Distances were enormous.

Bases were often separated by hundreds or thousands of miles.

This placed enormous emphasis on range.

The B-17 and B-24 were important early in the Pacific.

The B-25 became particularly useful for medium-range operations.

But the ultimate American Pacific bomber was the B-29 Superfortress.

The B-29’s extraordinary range allowed it to attack Japan from bases in the Marianas.

Initially, American commanders attempted high-altitude daylight precision bombing.

But Japanese weather conditions and the jet stream made this difficult.

General Curtis LeMay eventually shifted to low-level nighttime incendiary bombing.

The results were devastating.

Japanese cities, many of which contained large numbers of wooden buildings, were extremely vulnerable to incendiary weapons.

The March 1945 firebombing of Tokyo killed enormous numbers of civilians and demonstrated the destructive power of mass aerial bombardment.

The B-29 ultimately carried the atomic bombs used against Hiroshima and Nagasaki.

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How Aircraft Design Followed Strategy

The evolution of bomber aircraft closely paralleled the changing nature of the war.

Early Bombers

Early-war bombers tended to be relatively small twin-engine aircraft.

Examples included:

• Blenheim
• Hampden
• Battle
• Whitley
• A-20

They were intended for relatively short-range operations.

But they quickly became vulnerable to modern fighters.

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Heavy Bombers

The response was the four-engine heavy bomber.

Examples included:

• Lancaster
• Halifax
• Stirling
• B-17
• B-24
• B-29
• Il-4

These aircraft had greater range, larger bomb loads, and more defensive equipment.

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Faster Bombers

Another solution was simply to make bombers faster.

The Mosquito demonstrated how effective this approach could be.

Its speed allowed it to operate at lower risk without relying on enormous quantities of defensive armament.

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Better Defensive Armament

Aircraft such as the B-17 and B-24 were designed with numerous machine guns.

The assumption was that bomber formations could protect themselves.

Experience demonstrated the limitations of this concept.

The answer eventually became fighter escort.

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Better Engines

As engines became more powerful, aircraft could carry:

• More bombs
• More fuel
• More armor
• More equipment

while maintaining useful performance.

This was one reason the later-war bombers were so much more capable than their predecessors.

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Better Electronics

Perhaps the least visible but most important development was electronics.

Radar and radio-navigation systems transformed bombing.

Aircraft could navigate through darkness and clouds.

They could locate targets.

They could coordinate formations.

They could detect enemy aircraft.

The bomber of 1945 was therefore not merely a larger aircraft than the bomber of 1939.

It was a flying weapons system filled with electronics.

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A Summary of Major Allied Bomber Types

The following list provides a useful overview of the principal bomber and bomber-like aircraft discussed above.

United Kingdom

Heavy/strategic bombers:

• Armstrong Whitworth Whitley
• Vickers Wellington
• Handley Page Halifax
• Short Stirling
• Avro Lancaster

Medium/light/tactical bombers:

• Bristol Blenheim
• Fairey Battle
• de Havilland Mosquito
• Douglas Boston/A-20

Specialized aircraft:

• Bristol Beaufort
• Bristol Beaufighter
• Vickers Wellington

United States

Heavy bombers:

• Boeing B-17 Flying Fortress
• Consolidated B-24 Liberator
• Boeing B-29 Superfortress

Medium bombers:

• North American B-25 Mitchell
• Martin B-26 Marauder

Light/attack bombers:

• Douglas A-20 Havoc
• Douglas A-26 Invader

Soviet Union

Heavy/long-range bombers:

• Ilyushin Il-4
• Pe-8

Medium/light bombers:

• Petlyakov Pe-2
• Tupolev Tu-2
• Tupolev SB

Ground-attack aircraft:

• Ilyushin Il-2 Shturmovik

Canada

Canada primarily operated British and American designs, including:

• Wellington
• Hampden
• Lancaster
• Anson
• Bolingbroke
• Hudson
• Mitchell
• Mosquito

Australia

Principal Australian bomber/strike types included:

• Bristol Beaufort
• Bristol Blenheim
• Lockheed Hudson
• Vickers Wellington
• North American B-25 Mitchell
• Douglas Boston

Other Allied Air Forces

Other Allied nations operated aircraft such as:

• Wellington
• Halifax
• Lancaster
• Boston
• Hudson
• Baltimore
• Ventura
• Marauder

often as components of RAF, Commonwealth, Soviet, or American formations.

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The Bomber War’s Controversial Legacy

Strategic bombing remains one of the most controversial aspects of the Second World War.

The Allies destroyed enormous portions of German and Japanese cities.

Hundreds of thousands of civilians were killed by bombing.

Cities such as Hamburg, Dresden, Tokyo, and many others suffered catastrophic destruction.

There is continuing debate among historians over the military effectiveness of some bombing campaigns, particularly area bombing.

But there is much less doubt about the overall importance of air power.

Bombing disrupted transportation.

It destroyed factories.

It forced Germany to divert enormous resources toward air defense.

It compelled the Germans to build thousands of anti-aircraft guns.

It tied up millions of workers.

And Allied air superiority eventually made movement by German forces increasingly dangerous.

The bombing campaign therefore needs to be evaluated not merely by asking, “How many factories did the bombs destroy?”

A better question is:

“How did air power change the entire German war economy and military system?”

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Conclusion

The history of Allied bombers during the Second World War is really the story of the transformation of air power.

In 1939, many military planners still imagined the bomber primarily as an independent weapon capable of striking deep behind enemy lines.

By 1945, successful bombing depended upon an elaborate system involving: aircraft + fighter escorts + radar + navigation + intelligence + weather forecasting + logistics + industrial production.

British aircraft such as the Lancaster and Halifax made sustained strategic bombing of Germany possible.

American aircraft such as the B-17 and B-24 demonstrated the possibilities—and limitations—of daylight precision bombing.

The B-29 represented the ultimate development of the piston-engine heavy bomber and introduced a new era when it delivered the atomic bombs.

The Soviet Pe-2 and Tu-2 demonstrated the importance of tactical and operational bombing in supporting a massive land war.

Aircraft such as the Mosquito demonstrated that speed could sometimes be more valuable than defensive armament.

And aircraft such as the Il-2 demonstrated that the most important bombing mission could sometimes be only a few hundred yards ahead of an advancing army.

The bomber therefore evolved alongside the war itself.

In 1939, the bomber was expected to win wars by itself. By 1945, it had become one component of an integrated air power system.

That transformation would shape military aviation for the rest of the twentieth century—and eventually lead to the development of the jet bomber, strategic nuclear bomber, cruise missile, and modern precision-strike aircraft.