Boeing B-17 Flying Fortress

The B-17, nick-named the "Flying Fortress" was a heavy bomber that was the workhorse, along with the B-24 of America's strategic bombing of Germany in World War II. Over 12,000 Fortresses were built by Boeing. They were mainly deployed in Europe, flying from the 8th Air Force in England and the 15th Air Force in the Mediterranean. Their mission was strategic bombing.

Although originally designed in 1934, it was ahead of its time and proved a highly effective heavy bomber. A policy of continuous improvements added power gun turrets, bullet-proof glass, self-sealing fuel tanks, high-altitude oxygen systems, enlarged wing and tail surfaces, better radios, and ground- scanning radar. The power plant was upgraded with turbo- superchargers and 1,200 horsepower Wright Cyclone engines operating on 100 octane fuel (and later, 110/145 grade). The service ceiling rose to 35,000 feet, the range to 3,300 miles with a 4,000 pound payload. The Army Air Forces (AAF) considered the B-17 the perfect embodiment of its strategic bombing doctrine because of its long-range, its ability to defend itself, and its highly accurate Norden bomb-sight.

Aiming the bombs

The Norden bomb sight allowed daylight precision bombing of specific targets like factories. It worked well enough in leisurely practice runs in sunny California at 10,000 feet with no flak or enemy planes. Over German airspace, in bad weather at 20,000 feet with shells exploding all around and enemy fighters a constant threat, the B-17 had at most 30 seconds over the target. "The flak is murder," the pilots said. "If you fly straight and level through it for more than ten seconds, you're a dead duck."

Navigators found it very difficult to find the target in the first place. Navigation errors often put streams of 500 bombers many miles the wrong direction. At high altitude, with the usual cloud cover, it was nearly impossible to identify urban landmarks visually. On clear nights camouflage and dummy cities confused the navigators. H2X, an American adaptation of the British radar system H2S, provided a crude mapping of the ground through cloud cover. It helped locate targets, but beginners' luck in its early trials gave planners a much exaggerated estimate of the accuracy the Flying Fortress could achieve. In late 1943, one bomber in 25 hit within one mile of the aiming point, and only one in 5 even got within five miles. If the aiming point was a factory or railroad yard, fewer than 10% of the bombs that did land there would do any real damage. Bombs that missed and landed in residential areas were just like the RAF's; they would destroy apartments, but the residents were usually safe in underground shelters.

Raids

General Ira Eaker's Eighth Air Force first launched its heavy bombers against Hitler in August, 1942; the first year it made 83 major missions aimed at France, Holland, and the German cities closest to the English Channel. In August? 1943, Eaker sent 376 B-17s against the vital ball bearing factories at Schweinfurt and the Messerschmitt factory at Regensburg. Both small cities were located deep in Germany, far out of range of the P-47 and Spitfire fighters that normally escorted the bombers. German fighters and flak downed 60 bombers--a half dozen more raids like that and the 8th Air Force would cease to exist. After 30 more peripheral raids the Eighth tried Schweinfurt again in October, and again 60 Flying Fortresses (out of 320) were shot down. Accuracy was good despite the fierce resistance, and damage was heavy. The Germans took several months to rebuild (and to disperse critical plants so one raid would not prove fatal.) An effort to knock out the oil refineries at Ploesti, Romania, which provided a third of Nazi oil, cost 54 out of 177 B-24 Liberators. However, the daring raid at very low level (100 to 300 feet) destroyed 40% of Ploesti's capacity. German repair crews made unexpectedly speedy repairs.

German defenses

The lessons were a profound blow to American strategic bombing doctrines-- the British warnings about the devastation fighters could wreak on unescorted daytime bombers had proven correct. Luftwaffe clearly had air superiority over the Nazi heartland, unescorted bombers would suffer unacceptably high losses, and even severe damage could be quickly repaired. In daylight, large formations of several hundred B-17s were easily spotted. For self-defense each Flying Fortress had 13 50-calibre machine guns, and flew in loose formations of 6 planes, each covering the others. In 1942-43 the Luftwaffe proved the Fortresses were vulnerable. Unexpectedly heavy German flak defenses disrupted formations, and damaged on average one-fourth of the bombers in each mission. Berlin was surrounded by an outer searchlight belt 60 miles in diameter, and a flak area 40 miles across. The searchlights helped the guns locate their targets and also blinded the navigators. Three massive 120-foot flak towers resembling medieval castles protected central Berlin with 8 128mm high velocity guns each. They fired a salvo every 90 seconds that created a killing window 260 yards across in the path of the bombers. Hit by flak, some bombers crashed, while others fell out of formation; the stragglers were easy prey for large fighters with heavy cannons and rockets.

The Luftwaffe moved its best pilots fighters from the Eastern Front to defense of the homeland. Improved German radar, new airfields, and centralized ground control allowed groups of fighters to be quickly vectored into the predicted flight path of the Allied bombers. Luftwaffe ace Egon Mayer demonstrated the best way to attack was head-on ("Twelve O'Clock High!") because the very fast closing speed gave the B-17 gunners only a split second to aim, while the fighter pilot could aim his machine guns by pointing his entire aircraft at the bomber. The B-17 loss rate climbed from 3.5% per sortie in 1942 to 5% in early 1943. The B-17 was a robust plane able to withstand heavy punishment, but when 5% were lost in a single mission, the life expectancy per bomber was a mere 13 missions. The Luftwaffe was winning this war of attrition. New defensive 27 techniques included forward-firing chin turrets, tighter formations of 18 planes, and deceptive diversionary attacks; they were not enough.