The Boeing B-17 Fortress is now most often remembered as one of the great successes of World War 2. It is usually forgotten that the Fortress' combat debut—with Britain's Royal Air Force—was anything but auspicious. A combination of doctrinaire attachment to pre-war theories and a perhaps understandably patronizing attitude towards the advice offered by the as-yet untested US Army Air Force led to a hurried, premature deployment, serviceability problems, and heavy losses on operations.
In 1940, a British Purchasing Commission was established in the still nominally neutral United States for the purpose of obtaining war materiel, particularly aircraft. In addition to myriad Curtiss P-40s and Lockheed Hudsons, British representatives were anxious to obtain examples of Boeing's B-17 for use as high-altitude, daylight precision bombers.
In keeping with advanced, pre-war thinking on bomber vulnerability and disastrous experiences operating medium-altitude Blenheim and Wellington bombers in daylight early in the war, the Royal Air Force viewed high-altitude operations as crucial to the strategic air offensive against Germany. In daylight, heavily laden, medium-altitude bombers were at the mercy of fighters that, given then-current technology, were always much faster and more maneuverable. The high-velocity shells fired by antiaircraft guns could never be outrun or out-maneuvered in any case. Nocturnal operations had been the answer to this problem in the First War—and would prove so again—but, in 1940, there were apparently insurmountable objections to night bombing. By night, bombers could seldom get anywhere close to a specified location: hitting a military target with sufficient accuracy seemed out of the question. Attempting to do so would, at best, fatally reduce the military effectiveness of the air campaign while causing heavy civilian casualties, in contravention of international treaties and accepted rules and usages of war (an objection that would evaporate soon enough). But, if the bomber could neither outrun the fighter and the gun nor hide from them under cover of darkness, it might be able to fly higher than they could reach. The most common German antiaircraft guns of the day—the 88-mm—was effective to about 25,000 ft (7692 m). Above that altitude, bombers should be relatively safe. While fighters could certainly reach the same altitudes as bombers, they would seldom have enough advanced warning to do so. Climbing to 25,000 ft or more would generally take longer than the bombers took to fly over the target.
Britain had advanced, pressurized and turbosupercharged bombers in the planning stages in 1940. But, given the Wellington's shortcomings in actions against the German fleet, the RAF felt that it could not wait. It needed an interim high-altitude bomber capable of carrying the war to the German heartland in 1941 while preparing the pilots and aircrew that would later fly British designs to still greater heights. It thus turned to the United States and the bomber that the latter planned to use for its own high-altitude daylight bombing aircraft: the B-17. Late in 1940, the British Purchasing Commission obtained twenty Boeing B-17C bombers from US Army stocks. The aircraft were transferred from their base at Langley Field in Virginia to the Army's primary technical center, Wright Field in Ohio, for necessary modifications. The bombers were hurriedly made as fit for combat as possible. Self-sealing fuel tanks were retrofitted and .50-cal (12.7-mm) machine guns installed. In the spring of 1941, they were ferried across the Atlantic via Gander, Newfoundland and Prestwick, Scotland.
Unfortunately, the British were laboring under a misconception: the B-17C was neither combat-ready nor capable of routine operation above 20,000 ft or so. Though structurally advanced and equipped with turbocharged engines capable of maintaining rated power at altitude, these early Fortresses were essentially service-test aircraft. While heavier guns and self-sealing tanks rectified some of their deficiencies, the defensive capabilities of the airplane were still extremely limited. The C-model bombers lacked the power turrets that were all but essential when wielding heavy .50-cal guns at 200-mph speeds in the debilitating cold and low-pressure encountered at high altitude. The number of guns was inadequate. USAAF B-17s were intended to operate in close formation, where each bomber's heavy battery of machine guns could provide mutual support for its neighbors: the B-17C could mount at most six .50-cal machine guns on cramped, badly-situated mountings. Defense against attack from below was, for instance, limited by the poor field of view and limited angles of fire provided by the ventral, bathtub-type gun position. The waist guns were not staggered, so the gunners interfered with each others' movements during a fight. The all-important tail was all but undefended. Moreover, the requirements for operating fleets of these complex, four-engined aircraft at extreme altitudes was still very little understood. Experience with the early service-test B-17s was just beginning to suggest solutions to the many mechanical and aeromedical problems presented by low atmospheric pressure and extreme cold. Future, full-production versions of the new bomber would incorporate significant changes in light of this experience. B-17Cs did not and could not.
USAAF officers conscientiously attempted to open English eyes to the operational deficiencies of the B-17C. The Americans warned that the lack of rear defense would, on its own, render the B-17C unfit for combat over Europe. The mechanical unreliability of early, limited-production aircraft and engines and their complex, unfamiliar maintenance requirements were certain to result in poor availability and high accident rates. High-altitude formation flying on oxygen alone was, moreover, a demanding, specialist skill that required a high degree of training, constant practice, and extensive support from flight surgeons, meteorologists, and a host of other technicians.. Experienced RAF aircrews could not simply be reassigned from less physically and mentally demanding operations without a lengthy, preliminary working up period. The forty B-17Cs should thus be reserved for training. By the time that the RAF had mastered the necessary new piloting and maintenance skills, the more capable, fully operational B-17E and F models would be available, and operations could begin on a sound footing.
RAF staff failed to take American advice. The war was going badly in 1941, the RAF's vaunted strategic bombing arm was proving all but impotent, and the low- and medium-altitude, daylight attacks it had trained for were proving suicidal. Any new equipment or technique that might vindicate the heavy bomber as a weapon of war was simply too tempting to forego, even in the near term. American recommendations were, moreover, naturally suspect, given the USAAF's lack of any contemporary combat experience, and there seemed little reason to think that the mutual defense offered by .50-cal machine guns would be so significantly more effective than the demonstrably inadequate protection offered by the RAF's existing .303-cal guns (this last suspicion would, in fact, be confirmed when the first unescorted formations of USAAF B-17E/Fs ventured over Europe in daylight). If altitude might on its own offer protection, it had to be tried.
The B-17Cs were thus delivered to an operational bomber unit, 90 Squadron at Watton (Norfolk). As a concession to the aircraft's role, the Fortresses were given experimental, high-altitude camouflage finishes based on the standard RAF day bomber scheme. All aircraft shared the standard upper-surface finish of dark green and dark earth. 
But the standard scheme's pale, greenish Sky undersurfaces were thought likely to offer too much contrast when seen against darker, stratospheric skies. The under surfaces of most of the aircraft were thus given a coat of deep-sky, a color specially developed for high-altitude operations. In most cases this was extended well up the sides of the fuselage, above the midline and used on the vertical tail surfaces as well. At least a few photographs appear to show a lighter color in use, however, with a more standard treatment of the fuselage and tail. This has been reported to be Azure, but might equally well have been the standard, slightly greenish Sky.
Hastily formulated operational doctrine called for individual Fortresses or small-formations to attack point targets from the highest attainable altitude. Dry-docked German capital ships and German-controlled port facilities and electrical generating plants were considered ideal objectives. High-altitude flight was still viewed as little more than a more rigorous variation on normal RAF operations, so it was decided that picked flight crews should be able to handle with little or no additional preparation. Candidate crew members were specially selected for experience and had to be less than 24 years old. They were subjected to a four hour ordeal in a decompression chamber at a pressure equivalent to the anticipated operational altitude, 35,000 ft (10,769 m). Those who passed this test were then presumed to be naturally resistant to the effects of altitude (the cumulative effects of repeated cycles of compression and decompression were, apparently, given little consideration). The best, most experienced mechanics and ground staff were likewise selected to work on what were assumed to be high-performance variations on aircraft technologies that the RAF had already mastered.
Unfortunately, American advice proved substantially correct in this instance. At cruising altitude, the crews had to endure appalling conditions. The aircraft were, of course, unpressurized. Crews suffered severely from altitude-related illnesses that, in hindsight, seem consistent with decompression sickness and high-altitude pulmonary and cerebral edema (swelling in the brain and lungs). The resulting headaches, vomiting, breathing difficulty, confusion, and occasional loss of consciousness are now recognized as symptoms of a life-threatening condition. But, lacking the advantages of hindsight and the more extensive aeromedical resources of the USAAF, the RAF saw such issues as annoyances to be overcome by perseverance. Many unexplained aircraft losses during training and combat might well be attributable to altitude-related, low-pressure injuries alone. The cold was, by comparison, less deadly but no less debilitating. Contrary to expectations, German fighters could reach the Fortresses' operating altitude, so guns had to be deployed and manned at all times over enemy territory. With the windows covering the gun positions open, temperatures inside the airplane fell as low as -50&#degree; C, causing frostbite injuries and severe loss of crew efficiency and alertness.
Mechanical difficulties proved no less daunting and, all too frequently, no less fatal. In the absence of adequate meteorological support and comprehensive high-altitude flight training, crews fell victim to unexpected icing at altitude, lost control, and crashed or broke up in flight. Crews failed to dilute engine oil with gasoline at extreme altitudes and temperatures, so oil thickened and solidified, raising oil pressure to catastrophic levels. Frozen oil, forced from breathers and ruptured oil seals, accumulated on tail surfaces, locking controls and causing severe vibrations. Chunks of frozen oil broke off and damaged airframe components. Improperly prepared guns and gun mounts froze up when oil-filled recoil buffers locked solid and firing mechanisms jammed on congealed grease. Immature, untested technology compounded these operational problems. Propeller pitch controllers locked solid in the cold, overspeeding engines and causing fires or high drag. Turbocharger regulators failed and wastegates jammed, causing overboost to the engines, runaway superchargers, fires, and turbocharger explosions. In the dry thin air above 25,000 ft, electrical equipment arced and shorted out. Oxygen systems failed: gaskets and connectors became brittle and cracked and passages became blocked with ice. Oxygen masks and flight clothing proved uncomfortable and ineffective.
Tactically, high-altitude small-formation attacks were a failure. While height should have offered some protection against fighters, the critical element of surprise was usually lost long before the bombers approached their targets. Weather reports were still based primarily on local observation rather than preliminary aerial reconnaissance, so they frequently failed to forecast the altitudes at which contrails were most likely to form. So, as often as not, the bombers were clearly visible as they crossed the coast and entered enemy-held territory. German interceptors generally had enough warning to climb to the Fortresses' altitude well before the latter arrived, even though most missions involved shallow penetrations of French territory or long, over-water strikes flights to relatively less well-defended targets, such as Narvik in Norway. Of the two aircraft despatched to attack the battlecruisers Scharnhorst and Gneisenau in Brest on 16 august 1941, one (serial number AN352, aircraft "D") came under attack shortly after bombing from 32,000 ft and was driven down to 8,000 ft before making its escape less than 30 miles from the English coast, where it crashlanded with three dead aboard. The aircraft was a total loss. Of four aircraft sent against the Admiral Scheer in Oslo harbor on 8 September, two were shot down over Narvik, soon after crossing the coast, a third limped home on two engines only to crashed and burn on landing, and the fourth failed to find the target. Poor results made these losses all the more telling. Those that did seldom had anything to show for it. Bombing accuracy proved significantly poorer than USAAF experts had predicted, even under ideal conditions: point targets, like drydocked battleships, could not be hit at all, much less damaged or destroyed. Conditions were, moreover, far from ideal on typical operations. Weather forecasts that accurately predicted conditions over a bomber's home airfield or at altitude failed to anticipate conditions over the target. Even thin, low cloud or a modest smoke screen could make the target unrecognizable from 35,000 ft.
After 25 September 1941, 90 Squadron stood down from operations after barely five months and only 23 missions. In this brief time, five aircraft were destroyed in combat and four more were lost to accidents, malfunctions, and inexperience. Worse still, only 26 of the 48 total sorties flown resulted in bombs dropped on a primary or secondary target. No air force could long accept such losses in exchange for so little. The Fortress was deemed unsuitable for European conditions, and the surviving B-17Cs were sent to the Middle East as night bombers. The forthcoming B-17Es, -Fs, and -Gs would now serve the RAF as maritime reconnaissance aircraft or electronic jamming aircraft, not as day bombers.
The RAF's abandonment of the B-17 and, with it, of the day-bomber marked a watershed of sorts in the dreadfulness of modern warfare: the end of civilized Europe's brief flirtation with humane, legally circumscribed combat. Daylight precision strategic bombing had been the product of an attempt to reconcile the new technology of air warfare with emerging, late nineteenth- and early twentieth-century standards of wartime conduct. During the First World War, indiscriminate German shelling and bombing of populated areas in the vicinity of military targets had earned widespread condemnation, and idealistic interwar planners in America and Britain had looked to technology for assurances that only the actual military objective would be hit. Now, in British eyes at least, that technology had failed, just as a worsening war situation made humanitarian arguments seem ever less compelling. While the Americans would struggle on with the precision bombing concept for a few more years, until General Lemay's controversial night offensive against Japan's cities, Britain's Bomber Command now adopted a new doctrine: Area Bombing. Area Bombing adapted policy to the limitations of technology, rather than the reverse. Since precise high-altitude navigation and targeting were beyond the current state of the art, bombers would pound the general area surrounding their target—in effect, an entire city—by night, from low altitude, using incendiary bombs. Henceforth, civilian populations—the loyal citizens that staffed munitions factories and bred soldiers—would be the target of strategic air power.