When World War II began, only two nations had a coherent and committed strategic bombing program: Great Britain and the United States. Although most states with advanced militaries had interest in powerful airpower, continental concerns, resource limitations, or misguided procurement policies hindered most aspirants to powerful long-range bombing forces. Only relatively protected naval powers such as the United States and Britain could afford to focus so much attention on strategic bombing, lured by the strong political appeal of its promise of quick victory at relatively low cost. Both efforts had roots in the experience of the Royal Air Force (RAF) in World War I, when Sir Hugh Trenchard developed tactics and policies for the world's first independent air service and when talented subordinates such as Hardinge Goulburn Giffard, 1st Viscount Tiverton (subsequently 2nd Earl of Halsbury) pioneered target analysis for morale and material effects to assault the foundations of the German war economy. Although airmen in both countries became aware of the ideas of Giulio Douhet during the interwar years and used them to support arguments for strategic airpower, Douhet had little impact on the evolution of the RAF or the U.S. Army Air Corps.
The RAF continued to pursue Trenchard's ideal of a massive aerial offensive, assisted by politicians who were willing to fund an aerial deterrent instead of large expensive land armies that could become involved in more bloody continental wars. However, targeting priorities remained vague, and the war would soon reveal the large gap between claims and capabilities.
The Americans took a different approach that can be traced back to Tiverton's precedents. Although the subordinate army air service's primary mission remained ground support, a group of smart young officers at the Air Corps Tactical School (ACTS) developed a theory of precision daylight bombing of carefully selected targets in the industrial and service systems of enemy economies. Pinning their hopes on the capabilities of new aircraft such as the B-17 Flying Fortress, these airmen expected unescorted self-defending bombers to destroy vital nodes of the enemy's war economy that would grind it to a halt.
Bombing examples before and during the early days of World War II—in Spain and China and even the German Blitz on London—appeared to demonstrate the ineffectiveness and drawbacks of indiscriminate attacks on cities and to support the superiority of precision tactics. When President Franklin D. Roosevelt asked the army and navy for munitions estimates for a potential war in 1941, many of those ACTS instructors had joined the Air Staff in Washington. They soon developed a plan called AWPD/1 that envisioned a precision bombing campaign as a key component of the American war effort. When a larger plan that included AWPD/1 was accepted, the U.S. Army Air Forces (USAAF) finally had a justification for pursuing its own independent strategic bombing. They also found it difficult to put theory into practice.
Early British attacks moved from a Tivertonian focus on key systems like power plants or oil to a more Trenchardian reliance on widespread morale effects. Daylight raids proved deadly for RAF Bomber Command, revealing critical deficiencies in the number and quality of their bombers. Operations shifted to the nighttime, but the August 1941 Butt Report concluded that only about one in five aircrews were bombing within five miles of their intended targets. Adapting to the reality of their capabilities, in February 1942 Bomber Command was directed to attack area targets—that is, cities—with the objective of undermining German civilian morale, particularly that of industrial workers. Under the direction of Air Chief Marshal Sir Arthur Harris, Bomber Command built up its strength and obtained better aircraft, especially Halifax and Lancaster four-engine bombers. On 30 May 1942, Bomber Command mounted the first "thousand bomber raid" on Cologne, and in July 1943 it achieved the first bombing-induced firestorm against Hamburg, killing about 45,000 people. However German night defenses also adapted. When Harris decided to mount a full-scale assault on Berlin in late 1943, the Luftwaffe shot down so many British aircraft, and bombing results were so disappointing, that the utility of the whole night area campaign was brought into question.
Meanwhile, the Americans had also encountered difficulties. At Casablanca in January 1943, Allied leaders had agreed to a Combined Bomber Offensive (CBO) of round-the-clock attacks. It was rather poorly coordinated, but it did allow each air force to pursue its preferred approach. The most significant USAAF strategic attack of that year was General James Doolittle's July 1943 attack on Rome from North Africa, which heavily damaged the marshaling yards, limited collateral damage with impressive accuracy, and contributed to the fall of Benito Mussolini's government. Elements of the Eighth Air Force began bombing the continent from England in August 1942, although they did not fly deep penetration raids into central and eastern Germany until a year later. Losses among unescorted B-17 and B-24 "Liberator" bombers were horrendous, especially during attacks against ball-bearing plants at Schweinfurt in August and October 1943. Although the Fifteenth Air Force in Italy joined the daylight campaign in November 1943, the Americans were unable to sustain such attrition. By the end of the year, such deep attacks on Germany were suspended, and it appeared that the Luftwaffe was on the verge of winning the strategic air war in Europe.
Everything changed, however, with the advent of the Allied long-range escort fighter, most notably the P-51 "Mustang." In mid-February 1944, the U.S. Strategic Air Forces (USSTAF) began their "Big Week" attacks against German aircraft factories. The air battles that ensued decimated the Luftwaffe, and by the time of the D-day landings in June, the Allies achieved air supremacy over France and air superiority over Germany. The escort fighters began by sticking close to their bombers, but they proved most effective when they were released to sweep against enemy aircraft in the air and on the ground. Because of the American adoption of radar-directed bombing methods through overcast skies, the Germans had little respite even in poor weather, and their losses were increased by many accidents. Although the strategic bombers had an initial priority to operations in support of the coming invasion, Allied airpower had built up to the point that USSTAF commander General Carl Spaatz could begin sustained attacks against oil targets in May. By the fall of 1944, Luftwaffe and Wehrmacht operations were severely crippled by fuel shortages, and concentrated attacks against transportation networks further limited German mobility and economic activity.
During this period, Harris resisted diversions against "panacea targets" such as oil and remained committed to "dehousing" German workers. However, British bombers did sometimes assist with attacks on oil and transportation targets, and their larger loads of bombs could cause considerable damage. The RAF greatly improved its ability to navigate and bomb at night or in bad weather, and it usually achieved greater accuracy than the Americans under such conditions. Even in clear weather, precision bombing did not approach the image often portrayed in the press of bombs dropping down smokestacks. Usually, all aircraft in the B-17 and B-24 formations dropped their loads together, with intervals set between bombs so they would fall a few hundred feet apart. The pattern therefore covered a wide area. As USSTAF strength increased and targets became scarcer, planners became more tolerant of civilian casualties, adopting less accurate radar-directed bombardment methods in bad weather and hitting transportation objectives in city centers.
At least in Europe, American air leaders remained committed to attacks aimed primarily at economic and military targets instead of at civilian morale, a policy that sometimes caused friction with their British allies. There were also differences over bombing in occupied countries, where the British were particularly sensitive to political repercussions. The Americans were willing to bomb any Axis factory regardless of the nationality of the workers, whereas the British preferred to strike any German anywhere. The British also favored heavy attacks on the capitals of Axis allies in the Balkans, although the Americans successfully blocked what they saw as an inefficient and ineffective diversion of valuable airpower. Debates about the relative success and morality of RAF and USAAF bombing have continued to the present day.
The differing national approaches also played a role as the war in Europe approached its end, and both air forces sought an aerial death blow to finish the war. The British plan, code-named thunderclap, was based on shattering morale by destroying Berlin. That major assault was conducted by the Eighth Air Force on 3 February 1945. Allied concerns about assisting the Soviet advance helped produce the firestorm that devastated Dresden 10 days later. The corresponding American plan, code-named clarion, aimed to awe the German populace with widespread attacks on targets in every village. It was eventually changed into primarily a transportation assault because of concerns for efficiency, public image, and even morality. The controversy in Great Britain over the Dresden attack was one factor in the suspension of the strategic air war against Germany in April, although it was not as important as the simple fact that Allied bombing forces were running out of suitable targets.
American air leaders such as USAAF commanding General Henry H. "Hap" Arnold, who had hoped to build support for service independence by demonstrating the ability of air forces to win wars on their own, still had a chance against Japan. The USAAF referred to the B-29 Superfortress either as a very heavy bomber or a very long range bomber, and by World War II standards it was assuredly both. Every theater wanted to receive the B-29s, but the aircraft's impressive capabilities and late availability destined it for the Pacific. The Joint Chiefs of Staff established the Twentieth Air Force and named Arnold its "executive agent" to command the B-29s. Although operational control of the aircraft supposedly remained in Washington, in practice the commanders of the subordinate XX and XXI Bomber Commands enjoyed a great deal of independence.
The XX Bomber Command, based in India and China, mounted its first raid against Japan in June 1944. Operation matterhorn had little success, even after Arnold assigned his leading troubleshooter, Curtis LeMay, to command it. Bases were too far from key Japanese targets, difficult to supply, and hard to protect from Japanese ground attacks. Additionally the B-29s had been deployed a year early, and testing had to be completed in combat.
More was expected from the XXI Bomber Command based in the Mariana Islands, which was within range of the most important enemy industrial complexes in Honshu. Initial attacks were launched from Saipan in November 1944, but again results were disappointing. Besides technical and logistical problems, the command faced severe weather over target areas that made normal high-altitude precision bombing impossible. Although the vulnerability of Japanese cities to fires was well known and had inspired some USAAF planning for incendiary bombing, there was no meaningful pressure from Washington for such tactics. Impatient, however, for a better payoff on a huge investment, Arnold decided in January 1945 to concentrate all the B-29s in the Marianas under LeMay. Although the feisty and innovative air commander received little specific guidance from Washington, LeMay knew that he, too, could be relieved if he proved ineffective.
After trying to make daylight precision bombing work, on his own initiative LeMay adopted a new approach to destroy key industrial targets. His first low-level night area incendiary raid in March 1945 was a spectacular military success, incinerating 16 square miles of Tokyo and killing 90,000 people. Although he would mount some periodic day and night precision attacks, the fire raids dominated LeMay's air campaign against Japan. Eventually, he burned 178 square miles of some 66 Japanese cities, killing hundreds of thousands of people and causing millions to flee to the countryside. B-29s also dropped the two atomic bombs on Hiroshima and Nagasaki. MacArthur's Far East Air Forces contributed three attacks against Kyushu before the Japanese surrender, but the last American bombs that fell on Japan came from the Twentieth Air Force. More than 1,000 planes hit Japan on 14 August, some even after the Japanese radio had announced acceptance of the terms of surrender.
Both the British and Americans conducted postwar assessments of the strategic bombing campaign. The massive U.S. Strategic Bombing Survey compiled an impressive collection of data, although differing personalities and agendas within the survey committees produced several conflicting conclusions. They agreed, however, that the American approach to targeting was superior to RAF area bombing. The British Bombing Survey Unit relied on the American data along with some of its own, but overall it was not as thorough or comprehensive. It was also critical of the city attacks, but it gave much credit to the RAF-USAAF campaign against transportation.
In retrospect, the most important contribution strategic bombing made in Europe was to defeat the Luftwaffe and ensure that when Allied troops driving across northwestern Europe saw aircraft, they could be certain the planes were friendly. The CBO did not prevent the late-mobilizing German economy from peaking in 1944, but the oil and transportation campaigns had a major impact on degrading it thereafter. Civilian morale did not break, but some British observers have noted that the city bombing motivated German industry to disperse, thus making it more vulnerable to transportation interdiction. More than 700,000 German civilians died from Allied bombing, about the same number who succumbed to the effects of the British naval blockade in World War I. The cost of the CBO was also high for the air forces involved. The USSTAF lost 9,949 bombers, 8,500 fighters, and 64,000 airmen killed. RAF Bomber Command lost 57,000 killed or missing from all causes. In the Pacific, the incendiary attacks and atomic bombs were an important component of the series of shocks that produced the Japanese surrender, although the significance of other factors such as the submarine and naval blockade, as well as Soviet entry into the war, cannot be underestimated.
The World War II strategic bombing experience had several legacies. In the United States, the new U.S. Air Force was born in 1947, espousing a doctrine of air warfare based on the perceived lessons of their air campaigns against Germany and Japan along with the awesome power of nuclear weapons. "Vertical" targeting approaches against key Soviet industries resembled the German oil and transportation attacks, whereas "horizontal" methods based on LeMay's incendiary campaign were aimed at Soviet industrial concentrations in cities. One planner described the Strategic Air Command's early war plans as "precision attacks with area weapons." Since that time, the U.S. Air Force has dedicated itself to the pursuit of real precision, and the extreme accuracy of its contemporary munitions as well as current targeting doctrines have roots in the ideas developed at ACTS in the 1930s. However, while Americans trumpet their ongoing commitment to the principles of precision bombing, the rest of the world also remembers the images of Tokyo, Hamburg, and Dresden. Conrad C. Crane
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Conrad C. Crane