Strategic Bombing during World War II was unlike anything the world had previously witnessed. The strategic bombing campaigns conducted by the Germans, British, Americans and Japanese used conventional weapons, firebombs, biological agents, and nuclear weapons.
The Blitz
The British had been deeply physiologically affected by the German strategic bombing campaign of World War I. It was the first time in hundreds of years that the British capital had been successfully attacked by an enemy. In the interwar years, British calculations of the likely effect of a strategic bombing from the data gathered during the German campaign suggested that the a strategic attack on an enemy's cities using the latest generation of bombers would knock an enemy out of the war without the need for the stalemate of trench warfare. This had been an important factor in the British adoption of appeasement of Adolf Hitler during the 1930s, because the destruction which it was believed would result from a strategic bombing campaign using conventional bombs and poison gas, was thought to be on a scale which would not be seen in reality until the atomic bomb was developed.
In the rush to rearm in the late 1930s, the British had concentrated their limited resources on fighters which were seen as a defensive measure rather than bombers which were perceived as an offensive weapon. So when the war broke out in 1939, Britain's RAF had just 488 bombers of all kinds, mostly obsolescent, with only about 60 of the capable new Vickers Wellington: many of the remainder had insufficient range to reach the Ruhr (let alone Berlin), had negligible defensive armament, and could not carry a useful payload. In any case, there were no effective bomb sights, very few bombs of a size that could cause significant damage, and even such obvious things as maps of Europe for navigating to and from the target were in severe shortage. Furthermore the sheer difficulty of navigating, by night, long distances to accurately attack small targets was completely underestimated.
Germany, in contrast, had abandoned plans to produce strategic bombers. With German technical resources already hard pressed to supply other needs, with the Luftwaffe being part of the German army, and with the benefit of practical experience of modern war in Spain, German planners focused on tactical bombers to act as airborne artillery for the army, and fighters to protect them. When the fighting for Western Europe began in earnest, all three major powers (Britain, Germany and France) concentrated on daylight tactical bombing. The German Stukas and medium bombers were highly effective; the French Air Force, torn by political intra-service conflict and a lack of logistical preparation, was largely unable to employ its large numbers of modern aircraft; and the British found that bravery was no substitute for proper training, doctrine, and equipment—British losses in the defense of France were catastrophic, and the results negligible. In that first year of the war, strategic bombing was almost forgotten. It was in a sense, however, the calm before the storm.
After the fall of Europe came the Battle of Britain. The major part of the battle (up until about September 1940) was almost entirely tactical: the Luftwaffe aimed to prepare the way for an invasion by ground troops (or else destroy the ability of the RAF to resist and perhaps bring about a negotiated peace on favourable terms). Not realizing how close they had already come to success, the Germans switched away from attacking airfields and strictly military targets to simply bombing cities, in particular London. Many other British cities were hit, including Liverpool, Bristol, Belfast, Cardiff, and Coventry. The given aim was strategic—to destroy ports and industrial installations—but there is no room to doubt that destroying the will of ordinary people to fight was a major factor, perhaps the major factor.
Gradually, in the face of heavy losses to fighters, anti-aircraft guns, and accidents, the Luftwaffe resorted to night bombing. Targeting had been a problem in daylight; by night it was much more so, and British civilian casualties were heavy. The expected collapse in civilian morale, however, did not eventuate; indeed, it is widely believed that the bombings had the opposite effect.
Over the next year, an escalating war of electronic technology developed. The defenders struggled to develop countermeasures (in particular, airborne radar), while German scientists improvised a series of radio navigation aids to help their navigators find targets in the dark and through overcasts.
The work of code breakers at Bletchley Park allowed the British to overhear virtually all of German transmissions and thus allocate their limited defenses to maximum effect. Despite causing a great deal of damage and sorely trying the civilian population, the defenses gradually became more formidable, and the need to divert as many squadrons as possible to the Eastern Front saw the Blitz gradually fade away into mere nuisance raids.
The British retaliation
Britain retaliated with its own night strategic bombing campaign, which built up from RAF Bomber Command's tiny beginnings in 1940 to truly massive strength by the end of the war. The effects of strategic bombing were very poorly understood at the time and grossly overrated. Particularly in the first two years of the campaign, few understood just how little damage was caused and how rapidly the Germans were able to replace lost production—despite the obvious lessons to be learned from the United Kingdom's own survival of the Blitz.
Mid-way through the air war, it slowly began to be realized that the campaign was having very little effect. Despite an ever-increasing tonnage of bombs dispatched, the inaccuracy of delivery was such that any bomb falling within five miles of the target was deemed a "hit" for statistical purposes, and even by this standard, many bombs missed.
These problems were dealt with in two ways: first the precision targeting of vital facilities (ball-bearing production in particular) was abandoned in favour of "area bombing"—a euphemism for simply aiming at entire cities in the hope of killing workers, destroying homes, and breaking civilian morale. This change of policy was agreed by the Cabinet in 1942 after a paper was presented by Professor Lindemann, the British government's leading scientific adviser with a seat in the Cabinet, proposing the area aerial bombing of Geman cities. Air Marshal Arthur "Bomber" Harris was appointed to carry out the task. Secondly, efforts were made to improve accuracy by crew training, electronic aids, and the creation of a "pathfinder" force to mark targets for the main force.
A very large proportion of the industrial production of the United Kingdom was harnessed to the task of creating a vast fleet of heavy bombers—so much so that other vital areas of war production were under-resourced, notably the development of effective tanks and above all the provision of long-range aircraft to safeguard Atlantic shipping from submarine attack. Until fairly late in the war—about 1944—the effect on German production was remarkably small and nowhere near enough to justify the colossal diversion of scarce Commonwealth resources. The effect on German allocation of forces, however, gradually became significant: every extra anti-aircraft battery and night fighter squadron was one less to fight Russian forces on the Eastern Front. The disruption of the German transporation system was extensive, but the German government managed its loses effectively.
American bombing campaign
Mid-way through the war, the United States Army Air Force arrived to begin its own strategic bombing campaign, which was conducted in daylight. In Europe, the American Eighth Air Force heavy bombers carried smaller payloads than British aircraft (because of the need for defensive armament) but were generally able to deliver them somewhat more accurately. USAAF leaders firmly held to the claim that they were conducting "precision" bombing of military targets for much of the war, and energetically refuted claims that they were simply bombing cities. In reality, the day bombing was "precision bombing" only in the sense that most bombs fell somewhere in or near the desired city, whereas the night bombing campaign rarely achieved even that. Nevertheless, the sheer tonnage of explosive delivered by day and by night was eventually sufficient to cause widespread damage, and, more importantly from a military point of view, force Germany to divert resources to counter it. This was to be the real significance of the Allied strategic bombing campaign—resource allocation.
The twin campaigns—the US by day, the Commonwealth by night—built up into massive bombing of German industrial areas, notably the Ruhr, followed by attacks directly on cities such as Hamburg and the more often-criticized bombing of Dresden.
Effectiveness during WWII
Despite its popularity with the military and politicians, strategic bombing has been criticized on practical grounds because it does not always work reliably, and on moral grounds because of the large civilian casualties that result.
For instance, the Strategic bombing survey conducted by the United States after World War II determined that German industrial production in aircraft, steel, armor, and other sectors had risen during the war despite strategic bombing. The attack on oil was more successful and contributed to the general collapse of Germany in 1945. That collapse in 1945 was so total that the survey concluded it was impossible to know what portion to attribute to the bombing and what to other factors.
However, German insiders credit the Allied Bombing offensive with severely handicapping them. Albert Speer, Hitler's minister of production, repeatedly said (both during and after the war) that the bombing caused crucial production problems. A particular example comes from Admiral Karl Dönitz, head of the U-Boat arm, later the entire Kriegsmarine (and, eventually, the entire Reich from Hitler's suicide to the surrender). Dönitz notes in his memoires that the failure to get the revolutionary type XXI U-boats (which could have completely altered the balance of power in the Battle of the Atlantic) into service was entirely a result of the bombing.
Much of the misunderstanding about the effectiveness of the bomber war comes from that oft-stated fact that German industrial production increased throughout the war. While this is true, it fails to note that production also increased in the United States, the United Kingdom, the Soviet Union, Canada and Australia. And, in all of those countries, the rate of production increased much more rapidly than Germany. Until late in the war, German factory workers only worked a single shift. Simply by going to three shifts, production could be tripled with no change to the infrastructure. However, attacks on the infrastructure were taking place. The attacks on Germany's canals and railroads made transportation of materials difficult at best. Increased industrial output in the face of a destroyed transportation infrastructure tends to be ineffective.
Effect on morale
Although designed to "break the enemy's will", the opposite often happens. The British did not crumble under the German Blitz and other air raids early in the war. British workers continued to work throughout the war and food and other basic supplies were available throughout.