World War II (1939–1945) involved sustained strategic bombing of railways, harbours, cities, workers' and civilian housing, and industrial districts in enemy territory. Strategic bombing as a military strategy is distinct both from close air support of ground forces and from tactical air power. During World War II, many military strategists of air power believed that air forces could win major victories by attacking industrial and political infrastructure, rather than purely military targets. Strategic bombing often involved bombing areas inhabited by civilians, and some campaigns were deliberately designed to target civilian populations in order to terrorize them or to weaken their morale. International law at the outset of World War II did not specifically forbid the aerial bombardment of cities – despite the prior occurrence of such bombing during World War I (1914–1918), the Spanish Civil War (1936–1939), and the Second Sino-Japanese War (1937–1945). Strategic bombing during World War II in Europe began on 1 September 1939 when Germany invaded Poland and the Luftwaffe (German Air Force) began bombing Polish cities and the civilian population in an aerial bombardment campaign. As the war continued to expand, bombing by both the Axis and the Allies increased significantly. The Royal Air Force, in retaliation for Luftwaffe attacks on the UK which started on 16 October 1939, began bombing military targets in Germany, commencing with the Luftwaffe seaplane air base at Hörnum on the 19–20 March 1940. In September 1940 the Luftwaffe began targeting British civilians in the Blitz. After the beginning of Operation Barbarossa in June 1941, the Luftwaffe attacked Soviet cities and infrastructure. From February 1942 onward, the British bombing campaign against Germany became even less restricted and increasingly targeted industrial sites and civilian areas. When the United States began flying bombing missions against Germany, it reinforced British efforts. The Allies attacked oil installations, and controversial firebombings took place against Hamburg (1943), Dresden (1945), and other German cities. In the Pacific War, the Japanese frequently bombed civilian populations as early as 1937–1938, such as in Shanghai and Chongqing. US air raids on Japan escalated from October 1944, culminating in widespread firebombing, and later in August 1945 with the atomic bombings of Hiroshima and Nagasaki. The effectiveness of the strategic bombing campaigns is controversial. Although they did not produce decisive military victories in themselves, some argue that strategic bombing of non-military targets significantly reduced enemy industrial capacity and production, and was vindicated by the surrender of Japan. Estimates of the death toll from strategic bombing range from hundreds of thousands to over a million. Millions of civilians were made homeless, and many major cities were destroyed, especially in Europe and Asia.
Legal considerations
The Hague Conventions of 1899 and 1907, which address the codes of wartime conduct on land and at sea, were adopted before the rise of air power. Despite repeated diplomatic attempts to update international humanitarian law to include aerial warfare, it was not updated before the outbreak of World War II. The absence of specific international humanitarian law did not mean aerial warfare was not covered under the laws of war, but rather that there was no general agreement of how to interpret those laws. This means that aerial bombardment of civilian areas in enemy territory by all major belligerents during World War II was not prohibited by positive or specific customary international humanitarian law. Many reasons exist for the absence of international law regarding aerial bombing in World War II. Most nations had refused to ratify such laws or agreements because of the vague or impractical wording in treaties such as the 1923 Hague Rules of Air Warfare. Also, the major powers' possession of newly developed advanced bombers was a great military advantage; they would be hard pressed to accept any negotiated limitations regarding this new weapon. In the absence of specific laws relating to aerial warfare, the belligerents' aerial forces at the start of World War II used the 1907 Hague Conventions—signed and ratified by most major powers—as the customary standard to govern their conduct in warfare, and these conventions were interpreted by both sides to allow the indiscriminate bombing of enemy cities throughout the war. General Telford Taylor, Chief Counsel for War Crimes at the Nuremberg Trials, wrote that:
If the first badly bombed cities—Warsaw, Rotterdam, Belgrade, and London—suffered at the hands of the Germans and not the Allies, nonetheless the ruins of German and Japanese cities were the results not of reprisal but of deliberate policy, and bore witness that aerial bombardment of cities and factories has become a recognized part of modern warfare as carried out by all nations. Article 25 of the 1899 and 1907 Hague Conventions on Land Warfare also did not provide a clear guideline on the extent to which civilians may be spared; the same can be held for naval forces. Consequently, cyclical arguments, such as those advanced by Italian general and air power theorist Giulio Douhet, do not appear to violate any of the convention's provisions. Due to these reasons, the Allies at the Nuremberg and Tokyo Trials never criminalized aerial bombardment of non-combatant targets and Axis leaders who ordered a similar type of practice were not prosecuted. Chris Jochnick and Roger Normand in their article The Legitimation of Violence 1: A Critical History of the Laws of War explains that: "By leaving out morale bombing and other attacks on civilians unchallenged, the Tribunal conferred legal legitimacy on such practices."
== Ethical considerations == The concept of strategic bombing and its wide-scale implementation during WWII led to a post-war debate if it was moral. Three separate lines of ethical reasoning emerged. The first was based on the Just War theory and emphasized that noncombatants possess an inherent right to be spared from the harm of war and should not be intentionally targeted. John C. Ford, SJ, made such an argument in an article in 1944. Noncombatant immunity and proportionality in use of force were insisted upon. The second approach was grounded in the so-called "industrial web theory" that proposed to concentrate on destroying enemy military, industrial, and economic infrastructure instead of forces in the field as the fastest way to win the war. Proponents of this approach argued that civilian deaths inflicted by strategic bombing of the cities during the WWII were justified in the sense that they allowed a shortening of the war and thus helped to avoid many more casualties. The third approach was demonstrated by Michael Walzer in his Just and Unjust Wars (1977). Walzer formulated the so-called "supreme emergency" thesis. While agreeing in general with prior Just War theoretical postulates, he came to a conclusion that a grave threat to a moral order would justify the use of an indiscriminate force.
Air Marshal Sir Robert Saundby concluded his analysis of the ethics of bombing by these words, A study of the ethics of bombing cannot fail to remind one that man is an illogical creature, still far more swayed by emotion than by calm reason. Man has wonderful powers of self-deception, and of the uncritical suppression of unwelcome facts; he is still capable of believing what he wants to believe, in the face of overwhelming evidence to the contrary. Indeed, there are none so blind as will not see, or so deaf as will not hear. It is, therefore, no doubt unrealistic to hope for the general acceptance of rational views about such an emotive subject as the ethics of air bombardment.
Europe
=== Policy at the start of the war === Before World War II began, the rapid pace of aviation technology created a belief that groups of bombers would be capable of devastating cities. For example, British Prime Minister Stanley Baldwin warned in 1932, "The bomber will always get through." When the war began on 1 September 1939 with Germany's invasion of Poland, Franklin D. Roosevelt, President of the armed neutralitarian United States, issued an appeal to the major belligerents (Britain, France, Germany, and Poland) to confine their air raids to military targets, and "under no circumstances undertake bombardment from the air of civilian populations in unfortified cities". The British and French agreed to abide by the request, with the British reply undertaking to "confine bombardment to strictly military objectives upon the understanding that these same rules of warfare will be scrupulously observed by all their opponents". Germany also agreed to abide by Roosevelt's request and explained the bombing of Warsaw as within the agreement because it was supposedly a fortified city—Germany did not have a policy of targeting enemy civilians as part of their doctrine prior to World War II. The British Government's policy was formulated on 31 August 1939: if Germany initiated unrestricted air action, the RAF "should attack objectives vital to Germany's war effort, and in particular her oil resources". If the Luftwaffe confined attacks to purely military targets, the RAF should "launch an attack on the German fleet at Wilhelmshaven" and "attack warships at sea when found within range". The government communicated to their French allies the intention "not to initiate air action which might involve the risk of civilian casualties". While it was acknowledged bombing Germany would cause civilian casualties, the British government renounced deliberate bombing of civilian property, outside combat zones, as a military tactic. The British changed their policy on 15 May 1940, one day after the German bombing of Rotterdam, when the RAF was given permission to attack targets in the Ruhr Area, including oil plants and other civilian industrial targets which aided the German war effort, such as blast furnaces that at night were self-illuminating. The first RAF raid on the interior of Germany took place on the night of 15/16 May 1940 while the Battle of France was still continuing.
Early war in Europe
Poland
During the German invasion of Poland, the Luftwaffe engaged in massive air raids against Polish cities, bombing civilian infrastructure such as hospitals and targeting fleeing refugees. Notably, the Luftwaffe bombed the Polish capital of Warsaw, and the small towns Wieluń and Frampol. The bombing of Wieluń, one of the first military acts of World War II and the first major act of bombing, was carried out on a town that had little to no military value. Similarly, the bombing of Frampol has been described as an experiment to test the German tactics and weapons effectiveness. British historian Norman Davies writes in Europe at War 1939–1945: No Simple Victory: "Frampol was chosen partly because it was completely defenceless, and partly because its baroque street plan presented a perfect geometric grid for calculations and measurements." In his book, Augen am Himmel (Eyes on the Sky), Wolfgang Schreyer wrote:
Frampol was chosen as an experimental object, because test bombers, flying at low speed, weren't endangered by AA fire. Also, the centrally placed town hall was an ideal orientation point for the crews. We watched possibility of orientation after visible signs, and also the size of village, what guaranteed that bombs nevertheless fall down on Frampol. From one side it should make easier the note of probe, from second side it should confirm the efficiency of used bombs. The directives issued to the Luftwaffe for the Polish Campaign were to prevent the Polish Air Force from influencing the ground battles or attacking German territory. In addition, it was to support the advance of German ground forces through direct tactical and indirect air support with attacks against Polish mobilisation centres and thus delay an orderly Polish strategic concentration of forces and to deny mobility for Polish reinforcements through the destruction of strategic Polish rail routes.
Preparations were made for a concentrated attack (Operation Wasserkante) by all bomber forces against targets in Warsaw. However, the operation was cancelled, according to Polish professor Tomasz Szarota due to bad weather conditions, while German author Horst Boog claims it was possibly due to Roosevelt's plea to avoid civilian casualties; according to Boog the bombing of military and industrial targets within the Warsaw residential area called Praga was prohibited. Polish reports from the beginning of September note strafing of civilians by German attacks and bombing of cemeteries and marked hospitals (marking of hospitals proved counterproductive as German aircraft began to specifically target them, until hospitals were moved into the open to avoid such targeting), and indiscriminate attacks on fleeing civilians which according to Szarota was a direct violation of the Hague Convention. Warsaw was first attacked by German ground forces on 9 September and was put under siege on 13 September. German author Boog claims that with the arrival of German ground forces, the situation of Warsaw changed; under the Hague Convention, the city could be legitimately attacked as it was a defended city in the front line that refused calls to surrender. The bombing of the rail network, crossroads, and troop concentrations played havoc on Polish mobilisation, while attacks upon civilian and military targets in towns and cities disrupted command and control by wrecking the antiquated Polish signal network. Over a period of a few days, Luftwaffe numerical and technological superiority took its toll on the Polish Air Force. Polish Air Force bases across Poland were also subjected to Luftwaffe bombing from 1 September 1939. On 13 September, following orders of the Commander-in-Chief of the Luftwaffe (German Oberbefehlshaber der Luftwaffe (ObdL)) to launch an attack on Warsaw's Jewish Quarter, justified as being for unspecified crimes committed against German soldiers but probably in response to a recent defeat by Polish ground troops, and intended as a terror attack, 183 bomber sorties were flown with 50:50 load of high explosive and incendiary bombs, reportedly set the Jewish Quarter ablaze. On 22 September, Wolfram von Richthofen messaged, "Urgently request exploitation of last opportunity for large-scale experiment as devastation terror raid ... Every effort will be made to eradicate Warsaw completely". His request was rejected. However, Adolf Hitler issued an order to prevent civilians from leaving the city and to continue with the bombing, which he thought would encourage Polish surrender. On 14 September, the French Air attaché in Warsaw reported to Paris, "the German Air Force acted in accordance to the international laws of war [...] and bombed only targets of military nature. Therefore, there is no reason for French retorsions." That day – the Jewish New Year – the Germans concentrated again on the Warsaw's Jewish population, bombing the Jewish quarter and targeting synagogues. According to professor Szarota the report was inaccurate – as its author Armengaud didn't know about the most barbaric bombings like those in Wieluń or Kamieniec, left Poland on 12 September, and was motivated by his personal political goal to avoid French involvement in the war, in addition the report published in 1948 rather than in 1939.
Three days later, Warsaw was surrounded by the Wehrmacht, and hundreds of thousands of leaflets were dropped on the city, instructing citizens to evacuate the city pending a possible bomber attack. On 25 September the Luftwaffe flew 1,150 sorties and dropped 560 tonnes of high explosive and 72 tonnes of incendiaries. (Overall, incendiaries made up only 3% of the total tonnage dropped.) To conserve the strength of the bomber units for the upcoming Western campaign, the modern He 111 bombers were replaced by Ju 52 transports using "worse than primitive methods" for the bombing. Due to prevailing strong winds they achieved poor accuracy, even causing some casualties to besieging German troops. The only Polish raid against a target in Germany was executed by PZL.23 Karaś light bombers against a factory in Ohlau. The Polish air force left Poland on 18 September 1939 due to the Soviet attack on 17 September 1939, and imminent capture of the Polish airstrips and aircraft stationed in eastern parts of Poland. There was no exception; even Pursuit Brigade, an organic part of the defences of the Polish capital, Warsaw, was transferred to Lublin, one week into the war. There happened also a non-planned single bombing of the Free City of Danzig. On 7 September, at about 11 PM, a Polish Lublin R.XIII G seaplane was flying over the city, on a mission to attack the German Schleswig-Holstein battleship. However, the vessel had already left the city, so the seaplane flew over the center of Danzig, where it bombed and opened fire on the German troops celebrating the capitulation of the Polish garrison of Westerplatte.
==== The Western Front, 1939 to May 1940 ==== On 3 September 1939, following the German invasion of Poland, the United Kingdom and France declared war on Germany and the war in the West began. The RAF bombed German warships and light vessels in several harbours on 3 and 4 September. Eight German Kriegsmarine men were killed at Wilhelmshaven – the war's first casualties from British bombs; attacks on ships at Cuxhaven and Heligoland followed. The 1939 Battle of the Heligoland Bight showed the vulnerability of bombers to fighter attack. Germany's first strikes were not carried out until 16 and 17 October 1939, against the British fleet at Rosyth and Scapa Flow. Little activity followed. Meanwhile, attacks by the Royal Air Force dwindled to less than one a month. As the winter set in, both sides engaged in propaganda warfare, dropping leaflets on the populations below. The Phoney War continued. The British government banned attacks on land targets and German warships in port due to the risk of civilian casualties. For the Germans, the earliest directive from the Luftwaffe head Hermann Göring permitted restricted attacks upon warships anywhere, as well as upon troop transports at sea. However, Hitler's OKW Direktive Nr 2 and Luftwaffe Direktive Nr 2, prohibited attacks upon enemy naval forces unless the enemy bombed Germany first, noting, "the guiding principle must be not to provoke the initiation of aerial warfare on the part of Germany." After the Altmark incident, the Luftwaffe launched a strike against the British navy base at Scapa Flow on 16 March 1940, leading to the first British civilian death. A British attack followed three days later against the German airbase at Hörnum on the island of Sylt, hitting a hospital, although there were no casualties. The Germans retaliated with a naval raid. German bombing of France began on the night of 9/10 May. By 11 May, the French reported bombs dropped on Henin-Lietard, Bruay, Lens, La Fere, Loan, Nancy, Colmar, Pontoise, Lambersart, Lyons, Bouai, Hasebrouck, Doullens and Abbeville with at least 40 civilians killed. While Allied light and medium bombers attempted to delay the German invasion by striking at troop columns and bridges, the British War Cabinet gave permission for limited bombing raids against targets such as roads and railways west of the Rhine River.
Rotterdam Blitz
The Germans used the threat of bombing Rotterdam, the Netherlands, to try to get the Dutch to come to terms and surrender. After a second ultimatum had been issued by the Germans, it appeared their effort had failed and on 14 May 1940, Luftwaffe bombers were ordered to bomb Rotterdam in an effort to force the capitulation of the besieged city. The controversial bombing targeted the centre of the besieged city, instead of providing direct tactical support for the hard-pressed German 22nd Infantry Division (under Lt. Gen. von Sponeck, which had airlanded on 10 May) in combat with Dutch forces northwest of the city, and in the eastern part of the city at the Meuse river bridge. At the last minute, the Netherlands decided to submit and sent a plenipotentiary and other negotiators across to German lines. There was an attempt to call off the assault, but the bombing mission had already begun. In legal terms, the attack was performed against a defended part of a city vital for the military objectives and in the front-line, and the bombing respected Article 25 to 27 of the Hague Conventions on Land Warfare. Out of 100 Heinkel He 111s, 57 dropped their ordnance, a combined 97 tons of bombs. In the resulting fire 2.8 square kilometres (1.1 sq mi) of the city centre were devastated, including 21 churches and 4 hospitals. The strike killed between 800 and 1,000 civilians, wounded over 1,000, and made 78,000 homeless. In 2022, archival research showed a total of 1,150 to 1,250 civilians, and Dutch army and Nazi army personnel were killed during the Rotterdam Blitz. Nearly twenty-five thousand homes, 2,320 stores, 775 warehouses and 62 schools were destroyed. Whilst German historian Horst Boog says British propaganda inflated the number of civilian casualties by a factor of 30, contemporary newspaper reports show the Dutch legation in Paris initially estimated 100,000 people were killed, the Dutch legation in New York later issued a revised figure of 30,000. International news agencies widely reported these figures, portraying Rotterdam as a city mercilessly destroyed by terror bombing without regard for civilian life, with 30,000 dead lying under the ruins. It has been argued that the bombing was against well-defined targets, albeit in the middle of the city, and would have assisted the advancing German Army. The Germans had threatened to bomb Utrecht in the same fashion, and the Netherlands surrendered.
==== Allied response ==== Following the attack on Rotterdam, RAF Bomber Command was authorized to attack German targets east of the Rhine on 15 May 1940; the Air Ministry authorized Air Marshal Charles Portal to attack targets in the Ruhr, including oil plants and other civilian industrial targets which aided the German war effort, such as blast furnaces. The underlying motive for the attacks was to divert German air forces away from the land front. Churchill explained the rationale of his decision to his French counterparts in a letter dated the 16th: "I have examined today with the War Cabinet and all the experts the request which you made to me last night and this morning for further fighter squadrons. We are all agreed that it is better to draw the enemy on to this Island by striking at his vitals, and thus to aid the common cause." Due to the inadequate British bomb-sights the strikes that followed "had the effect of terror raids on towns and villages." On the night of 15/16 May, 96 bombers crossed the Rhine and attacked targets in Gelsenkirchen. 78 had been assigned oil targets, but only 24 claimed to have accomplished their objective. On the night of 17/18 May, RAF Bomber Command bombed oil installations in Hamburg and Bremen; the H.E. and 400 incendiaries dropped caused six large, one moderately large and twenty-nine small fires. As a result of the attack, 47 people were killed and 127 were wounded. Railway yards at Cologne were attacked on the same night. During May, Essen, Duisburg, Düsseldorf and Hanover were attacked in a similar fashion by Bomber Command. In June, attacks were made on Dortmund, Mannheim, Frankfurt and Bochum. At the time, Bomber Command lacked the necessary navigational and bombing technical background and the accuracy of the bombings during the night attacks was abysmal. Consequently, the bombs were usually scattered over a large area, causing an uproar in Germany. On the night of 7/8 June 1940 a single French Navy Farman F.223 aircraft bombed Berlin, the first Allied attack on the capital. Despite the British attacks on German cities, the Luftwaffe did not begin to attack military and economic targets in the UK until six weeks after the campaign in France was concluded.
The Battle of Britain and the Blitz
On 22 June 1940, France signed an armistice with Germany. Britain was determined to keep fighting. On 1 and 2 July, the British attacked the German warships Scharnhorst and Prinz Eugen in the port of Kiel and the next day, 16 RAF bombers attacked German train facilities in Hamm. The Battle of Britain began in early June 1940 with small scale bombing raids on Britain. These Störangriffe ("nuisance raids") were used to train bomber crews in both day and night attacks, to test defences and try out methods. These training flights continued through July and August, and into the first week of September. Hermann Göring's general order, issued on 30 June 1940, stated:
The war against England is to be restricted to destructive attacks against industry and air force targets which have weak defensive forces. ... The most thorough study of the target concerned, that is vital points of the target, is a pre-requisite for success. It is also stressed that every effort should be made to avoid unnecessary loss of life amongst the civilian population. The Kanalkampf of attacks on shipping and fighter skirmishes over the English Channel started on 4 July, and escalated on 10 July, a day which Dowding later proposed as the official start date for the Battle. Throughout the battle, Hitler called for the British to accept peace, but they refused to negotiate. Still hoping that the British would negotiate for peace, Hitler explicitly prohibited attacks on London and against civilians. Any airmen who, intentionally or unintentionally, violated this order were punished. Hitler's No. 17 Directive, issued 1 August 1940, established the conduct of war against Britain and specifically forbade the Luftwaffe from conducting terror raids. The Führer declared that terror attacks could only be a means of reprisal, as ordered by him.
On 6 August Göring finalised plans for "Operation Eagle Attack" with his commanders: destruction of RAF Fighter Command across the south of England was to take four days, then bombing of military and economic targets was to systematically extend up to the Midlands until daylight attacks could proceed unhindered over the whole of Britain, then a major attack was to be made on London causing a crisis with refugees when the intended Operation Sea Lion invasion was due to begin. On 8 August 1940, the Germans switched to raids on RAF fighter bases. To reduce losses, the Luftwaffe also began to use increasing numbers of bombers at night. From the night of 19/20 August night bombing targeted the aircraft industry, ports, harbours, and other strategic targets in towns and cities, including suburban areas around London. By the last week of August, over half the missions were flown under the cover of dark. On 24 August, several off-course German bombers accidentally bombed central areas of London. The next day, the RAF bombed Berlin for the first time, targeting Tempelhof airfield and the Siemens factories in Siemenstadt. These attacks were seen by the Germans as indiscriminate due to their inaccuracy, and this infuriated Hitler; he ordered that the 'night piracy of the British' be countered by a concentrated night offensive against the island, and especially London. In a public speech in Berlin on 4 September 1940, Hitler announced that:
The other night the English had bombed Berlin. So be it. But this is a game at which two can play. When the British Air Force drops 2000 or 3000 or 4000 kg of bombs, then we will drop 150 000, 180 000, 230 000, 300 000, 400 000 kg on a single night. When they declare they will attack our cities in great measure, we will eradicate their cities. The hour will come when one of us will break – and it will not be National Socialist Germany!
The Blitz was underway. Göring – at Kesselring's urging and with Hitler's support – turned to a massive assault on the British capital. On 7 September 318 bombers from the whole KG 53 supported by eight other Kampfgruppen, flew almost continuous sorties against London, the dock area which was already in flames from earlier daylight attacks. The attack of 7 September 1940 did not entirely step over the line into a clear terror bombing effort since its primary target was the London docks, but there was clearly an assumed hope of terrorizing the London population. Hitler himself hoped that the bombing of London would terrorize the population into submission. He stated that "If eight million [Londoners] go mad, it might very well turn into a catastrophe!". After that he believed "even a small invasion might go a long way". Another 250 bomber sorties were flown in the night. By the morning of 8 September 430 Londoners had been killed. The Luftwaffe issued a press notice announcing they had dropped more than 1,000,000 kilograms (1,100 short tons) of bombs on London in 24 hours. Many other British cities were hit in the nine-month Blitz, including Plymouth, Swansea, Birmingham, Sheffield, Liverpool, Southampton, Manchester, Bristol, Belfast, Cardiff, Clydebank, Kingston upon Hull and Coventry. Basil Collier, author of 'The Defence of the United Kingdom', the HMSO's official history, wrote:
Although the plan adopted by the Luftwaffe early in September had mentioned attacks on the population of large cities, detailed records of the raids made during the autumn and the winter of 1940–41 do not suggest that indiscriminate bombing of civilians was intended. The points of aim selected were largely factories and docks. Other objectives specifically allotted to bomber-crews included the City of London and the governmental quarter round Whitehall. In addition to the conclusions of Basil Collier to that effect there are also, for example, the 1949 memoirs of General Henry H. Arnold who had been in London in 1941 and supported Collier's estimate. Harris noted in 1947 that the Germans had failed to take the opportunity to destroy English cities by concentrated incendiary bombing. As the war continued, an escalating war of electronic technology developed. To counter German radio navigation aids, which helped their navigators find targets in the dark and through cloud cover, the British raced to work out the problems with countermeasures (most notably airborne radar, as well as highly effective deceptive beacons and jammers). Despite causing a great deal of damage and disrupting the daily lives of the civilian population, the bombing of Britain failed to have an impact. British air defenses became more formidable, and attacks tapered off as Germany abandoned its efforts against Britain and focused more on the Soviet Union. Operation Abigail Rachel, the bombing of Mannheim, was one of the first revenge bombings by the British against a German city on 16 December. The British had been waiting for the opportunity to experiment with such a raid aimed at creating a maximum of destruction in a selected town since the summer of 1940, and the opportunity was given after the German raid on Coventry. Internally it was declared to be a reprisal for Coventry and Southampton. The new bombing policy was officially ordered by Churchill at the start of December, on condition it receive no publicity and be considered an experiment. Target marking and most bombs missed the city centre. This led to the development of the bomber stream. Despite the lack of decisive success of this raid, approval was granted for further Abigails. This was the start of a British drift away from precision attacks on military targets and towards area bombing attacks on whole cities.
Germany later in the war
Goering's first chief of staff, Generalleutnant Walther Wever, was a big advocate of the Ural bomber program, but when he died in a flying accident in 1936, support for the strategic bomber program began to dwindle rapidly under Goering's influence. Under pressure from Goering, Albert Kesselring, Wever's replacement, opted for a medium, all-purpose, twin-engine tactical bomber. Erhard Milch, who strongly supported Goering's conceptions, was instrumental in the Luftwaffe's future. Milch believed that the German industry (in terms of raw materials and production capacity) could only produce 1,000 four-engine heavy bombers per year, but many times that number of twin-engine bombers. In spring of 1937, just when the Luftwaffe's own Technical Office had passed the Ju-89 and Do-19 heavy bomber models as ready for testing, Goering ordered a halt to all work on the four-engine strategic bomber program. However, in 1939 the Bomber B program sought to produce a twin-engined strategic bomber that could carry nearly-equivalent bombloads of Allied four-engined heavy bombers, but as an advanced development of the pre-war Schnellbomber concept. The Bomber B designs meant to achieve top level speeds of at least 600 km/h (370 mph). The Bomber B program went nowhere, as the intended designs required pairs of combat-reliable aviation engines of at least 1,500 kW (2,000 PS) apiece, something that the German aviation engine industry had serious problems in developing. A further design program was initiated in the late spring of 1942, to develop four-engine (and later six-engine) bombers with trans-Atlantic range to attack the continental United States and aptly named the Amerika Bomber. This also went nowhere, with only five prototype airframes from two design competitors getting airborne for testing, before the war's end.
The only heavy bomber design to see service with the Luftwaffe in World War II was the trouble-prone Heinkel He 177A. In the initial design of November 1937, the RLM had mistakenly decided that the He 177 should also have a medium angle "dive bombing" capability. Ernst Heinkel and Milch vehemently disagreed with this, but the requirement was not rescinded until September 1942 by Goering himself. The He 177A went into service in April 1942, despite an ongoing series of engine fires in the small batch of A-0 series production prototype aircraft. This deficiency, along with numerous, seriously deficient design features, led Goering to decry the He 177A's Daimler-Benz DB 606 powerplants to be nothing more than fire-prone, cumbersome "welded-together engines" in August of that year. Production of the B-series by Heinkel's only subcontractor for the Greif, Arado Flugzeugwerke, would not have started until November 1944, because of Arado's focus on the production of its own Arado Ar 234 jet-powered reconnaissance-bomber at the time. The July 1944-initiated Emergency Fighter Program (Jägernotprogramm), as well as the devastating effects of Allied bombing on the entire German aviation industry, prevented any production of the He 177B design. The He 177A entered service in April 1942. At this time, after a destructive RAF attack on Lübeck, Adolf Hitler ordered the Luftwaffe to retaliate with the so-called Baedeker Blitz:
The Führer has ordered that the air war against England be given a more aggressive stamp. Accordingly, when targets are being selected, preference is to be given to those where attacks are likely to have the greatest possible effect on civilian life. Besides raids on ports and industry, terror attacks of retaliatory nature are to be carried out against towns other than London. Minelaying is to be scaled down in favour of these attacks. In January 1944, a beleaguered Germany tried to strike a blow to British morale with terror bombing with Operation Steinbock, nicknamed the "Baby Blitz" by the British. At this stage of the war, Germany was critically short of heavy and medium bombers, with the added obstacles of a highly effective and sophisticated British air-defence system, and the increasing vulnerability of airfields in occupied Western Europe to Allied air attack making the effectiveness of German retaliation more doubtful. British historian Frederick Taylor asserts that "all sides bombed each other's cities during the war. Half a million Soviet citizens, for example, died from German bombing during the invasion and occupation of Russia. That's roughly equivalent to the number of German citizens who died from Allied raids." The Luftwaffe destroyed numerous Soviet cities through bombing, including Minsk, Sevastopol, and Stalingrad. 20,528 tons of bombs were dropped on Sevastopol in June 1942 alone. German bombing efforts on the Eastern Front dwarfed its commitments in the west. From 22 June 1941 to 30 April 1944, the Luftwaffe dropped 756,773 tonnes of bombs on the Eastern Front, a monthly average of 22,000 tonnes. German scientists had invented vengeance weapons – V-1 flying bombs and V-2 ballistic missiles – and these were used to launch an aerial assault on London and other cities in southern England from continental Europe. The campaign was much less destructive than the Blitz. As the Allies advanced across France and towards Germany from the West, Paris, Liège, Lille, and Antwerp also became targets. The British and US directed part of their strategic bombing effort to the eradication of "wonder weapon" threats in what was later known as Operation Crossbow. The development of the V2 was hit preemptively in Operation Hydra of August 1943 against Peenemunde research facility.
The British later in the war
The purpose of the area bombardment of cities was laid out in a British Air Staff paper, dated 23 September 1941:
The ultimate aim of an attack on a town area is to break the morale of the population which occupies it. To ensure this, we must achieve two things: first, we must make the town physically uninhabitable and, secondly, we must make the people conscious of constant personal danger. The immediate aim, is therefore, twofold, namely, to produce (i) destruction and (ii) fear of death. During the first few months of the area bombing campaign, an internal debate within the British government about the most effective use of the nation's limited resources in waging war on Germany continued. Should the Royal Air Force (RAF) be scaled back to allow more resources to go to the British Army and Royal Navy or should the strategic bombing option be followed and expanded? An influential paper was presented to support the bombing campaign by Professor Frederick Lindemann, the British government's leading scientific adviser, justifying the use of area bombing to "dehouse" the German workforce as the most effective way of reducing their morale and affecting enemy war production. Mr. Justice Singleton, a High Court Judge, was asked by the cabinet to look into the competing points of view. In his report, delivered on 20 May 1942, he concluded:
If Russia can hold Germany on land I doubt whether Germany will stand 12 or 18 months' continuous, intensified and increased bombing, affecting, as it must, her war production, her power of resistance, her industries and her will to resist (by which I mean morale). In the end, thanks in part to the dehousing paper, it was this view which prevailed and Bomber Command would remain an important component of the British war effort up to the end of World War II. A large proportion of the industrial production of the United Kingdom was harnessed to the task of creating a vast fleet of heavy bombers. Until 1944, the effect on German production was remarkably small and raised doubts whether it was wise to divert so much effort—the response being there was nowhere else the effort could have been applied, as readily, to greater effect.
Lindemann was liked and trusted by Winston Churchill, who appointed him the British government's leading scientific adviser with a seat in the Cabinet. In 1942, Lindemann presented the "dehousing paper" to the Cabinet showing the effect that intensive bombing of German cities could produce. It was accepted by the Cabinet, and Air Marshal Harris was appointed to carry out the task. It became an important part of the total war waged against Germany. Professor Lindemann's paper put forward the theory of attacking major industrial centres in order to deliberately destroy as many homes and houses as possible. Working-class homes were to be targeted because they had a higher density and fire storms were more likely. This would displace the German workforce and reduce their ability to work. His calculations (which were questioned at the time, in particular by Professor P. M. S. Blackett of the Admiralty operations research department, expressly refuting Lindemann's conclusions) showed the RAF's Bomber Command would be able to destroy the majority of German houses located in cities quite quickly. The plan was highly controversial even before it started, but the Cabinet thought that bombing was the only option available to directly attack Germany (as a major invasion of the continent was almost two years away), and the Soviets were demanding that the Western Allies do something to relieve the pressure on the Eastern Front. Few in Britain opposed this policy, but there were three notable opponents in Parliament, Bishop George Bell and the Labour MPs Richard Stokes and Alfred Salter.
On 14 February 1942, the area bombing directive was issued to Bomber Command. Bombing was to be "focused on the morale of the enemy civil population and in particular of the industrial workers." Though it was never explicitly declared, this was the nearest that the British got to a declaration of unrestricted aerial bombing – Directive 22 said "You are accordingly authorised to use your forces without restriction", and then listing a series of primary targets which included Dortmund, Essen, Duisburg, Düsseldorf, and Cologne. Secondary targets included Braunschweig, Lübeck, Rostock, Bremen, Kiel, Hanover, Frankfurt, Mannheim, Stuttgart, and Schweinfurt. The directive stated that "operations should now be focused on the morale of the enemy civilian population, and in particular, the industrial workers". Lest there be any confusion, Sir Charles Portal wrote to Air Chief Marshal Norman Bottomley on 15 February,
I suppose it is clear that the aiming points will be the built-up areas, and not, for instance, the dockyards or aircraft factories [...]. The first true practical demonstrations were on the night of 28 to 29 March 1942, when 234 aircraft bombed the port of Lübeck. This target was chosen not because it was a significant military target, but because it was expected to be particularly susceptible – in Harris's words it was "built more like a fire lighter than a city". The old timber structures burned well, and the raid destroyed most of the city's centre. A few days later, Rostock suffered the same fate.
At this stage of the air war, the most effective and disruptive examples of area bombing were the "thousand-bomber raids". Bomber Command was able by organization and drafting in as many aircraft as possible to assemble very large forces which could then attack a single area, overwhelming the defences. The aircraft would be staggered so that they would arrive over the target in succession: the new technique of the "bomber stream". On 30 May 1942, between 0047 and 0225 hours, in Operation Millennium 1,046 bombers dropped over 2,000 tons of high explosive and incendiaries on Cologne, and the resulting fires burned it from end to end. The damage inflicted was extensive. The fires could be seen 1,000 kilometres (600 mi) away at an altitude of 20,000 feet. Some 3,300 houses were destroyed, and 10,000 were damaged. 12,000 separate fires raged destroying 36 factories, damaging 270 more, and leaving 45,000 people with nowhere to live or to work. Only 384 civilians and 85 soldiers were killed, but thousands evacuated the city. Bomber Command lost 40 bombers. Two further thousand-bomber raids were conducted over Essen and Bremen, but neither so utterly shook both sides as the scale of the destruction at Cologne and Hamburg. The effects of the massive raids using a combination of blockbuster bombs (to blow off roofs) and incendiaries (to start fires in the exposed buildings) created firestorms in some cities. The most extreme examples of which were caused by Operation Gomorrah, the combined USAAF/RAF attack on Hamburg, (45,000 dead), attack on Kassel (10,000 dead), the attack on Darmstadt (12,500 dead), the attack on Pforzheim (21,200 dead), the attack on Swinemuende (23,000 dead) and the attack on Dresden (25,000 dead). According to economic historian Adam Tooze, in his book The Wages of Destruction: The Making and Breaking of the Nazi Economy, a turning point in the bomber offensive was reached in March 1943, during the Battle of the Ruhr. Over five months, 34,000 tons of bombs were dropped. Following the raids, steel production fell by 200,000 tons, making a shortfall of 400,000 tons. Speer acknowledged that the RAF were hitting the right targets, and raids severely disrupted his plans to increase production to meet increasing attritional needs. Between July 1943 and March 1944 there were no further increases in the output of aircraft. The bombing of Hamburg in 1943 also produced impressive results. Attacks on Tiger I heavy tank production, and of that of 88 mm guns, the most potent dual-purpose artillery piece in the Wehrmacht, meant that output of both was "set back for months". On top of this, some 62% of the population was dehoused causing more difficulties. However, RAF Bomber Command allowed itself to be distracted by Harris' desire for a war winning blow, and attempted the fruitless missions to destroy Berlin and end the war by spring, 1944. In October 1943, Harris urged the government to be honest with the public regarding the purpose of the bombing campaign. To Harris, his complete success at Hamburg confirmed the validity and necessity of his methods, and he urged that:
the aim of the Combined Bomber Offensive...should be unambiguously stated [as] the destruction of German cities, the killing of German workers, and the disruption of civilized life throughout Germany. He further said,
the destruction of houses, public utilities, transport and lives, the creation of a refugee problem on an unprecedented scale, and the breakdown of morale both at home and at the battle fronts by fear of extended and intensified bombing, are accepted and intended aims of our bombing policy. They are not by-products of attempts to hit factories.
By contrast, the United States Strategic Bombing Survey found attacks on waterways, beginning 23 September with strikes against the Dortmund-Ems Canal and Mittelland Canal, produced tremendous traffic problems on the Rhine River. It had immediate effects on shipments of goods, and especially coal deliveries, upon which Germany's economy depended. With no more additional effort, by February 1945, rail transport (which competed for coal) had seen its shipments cut by more than half, and by March, "except in limited areas, the coal supply had been eliminated". The devastating bombing raids of Dortmund on 12 March 1945 with 1,108 aircraft – 748 Lancasters, 292 Halifaxes, 68 de Havilland Mosquitos – was a record attack on a single target in the whole of World War II. More than 4,800 tons of bombs were dropped through the city centre and the south of the city and destroyed 98% of buildings.