B-17 Flying Fortress
B-17s at War
Boeing’s B-17 led the strategic bombing offensive against Germany, but at first, the company’s “Flying Fortress” name represented journalistic and advertising hyperbole. Before sustained daylight operations could be made, protection against enemy fighters had to be improved. Describing how the airmen fought their battles in the B-17 and other wartime bombers would fill whole books by itself; in our bibliography we list the best. For this chapter, we must be limited to identification of the major steps in weapons development.
The first Flying Fortress used in air combat was the nine-place B-17C with four Wright Cyclones, up to 800 pounds of armor, leak proof tanks, and the four gun blisters replaced by new openings for each .50-caliber gun. Flush panels were provided on the sides, another over the radio compartment, and a tub for the kneeling bottom gunner. A single .30-caliber gun could be fired from any of six sockets in the nose. Bomb bay capacity remained the same (4,992 pounds with eight 624-pound bombs) as on the YB-17.
Thirty-eight B-17Cs were ordered August 10, 1939, and Poland had been overrun by the Germans before this contract was approved on September 20 by the Secretary of War. The first B-17C flew July 21, 1940, and was retained by the company for tests, while the last was delivered by November 29.
Boeing had guaranteed a top speed of 274 mph at 15,000 feet and 300 mph at 25,000 feet at design weight with a normal 1,000 hp from the R-1820-65 engines, but the Army credited the B-17C with 323 mph when the B-2 turbosuperchargers boosted 1,200 hp at 25,000 feet. Twenty B-17Cs were sold to Britain as the Fortress I, and all were returned to Boeing in January 1941 to be modified to B-17D standards with seven guns and Goodrich self-sealing fuel tanks.
Forty-two more had been ordered April 17, 1940, but were redesignated B-17D on September 6. Delivered from February 3 to April 29, 1941, they could be distinguished from the Cs by their cowl flaps. Improved protection included a new self-sealing fuel tank system and paired guns in the belly and top positions to bring the total up to one .30-caliber and six .50-caliber guns with 500 rpg.
Britain’s own four-engine bomber in 1940, the Short Stirling, contrasted sharply with the B-17, for it carried 14,000 pounds of bombs and power-operated turrets, with a top speed of 260 mph and a ceiling of only 18,000 feet instead of the 37,000 feet of the American aircraft.
All British heavy bombers were then attacking at night, but a new squadron, No. 90, was selected to try day bombing from high-altitude to avoid AAA fire and fighter interception. The RAF Fortresses began arriving in Britain on April 14, 1941, fitted with Sperry bombsights, as the Norden sight was considered too secret for export. A Lend-lease contract made June 2, 1941, promised 300 B-17F-1s (Fortress II) to the RAF, if the first efforts succeeded.
“The desire to use an American bomber at the earliest opportunity is to be expected and has propaganda value”. But a secret memo on May 22 went on to warn “...that this aircraft has been given world-wide publicity, and if it fails...no hiding of the news will be possible and the whole world will know, with the expected effect on British and American prestige and morale.”
Results were disappointing, due to problems with freezing equipment and operation of the first turbosuperchargers in RAF service. Four 1,100-pound bombs were to be dropped from 30,000 feet from each Fortress on the first Wilhelmshaven raid on July 8, 1941, but mechanical difficulties hampered the mission. Three sent July 23 on aprestige raid to Berlin were turned back by the weather. Brest and Emden were attacked next, and on August 2, gunners downed a Bf 109F, the first such victory by an American heavy bomber. But two of the three Boeings near Oslo were destroyed by Bf 109T fighters on August 9th.
Raids from England ended by September 26 after 51 sorties, of which 27 had aborted. Seven B-17Cs had been lost during that time to accidents and enemy fighters, and few direct hits were confirmed.
Americans blamed this poor record on excessively high attack altitudes, and on not flying in formation to promote defensive firepower and a good bombing pattern; but it was evident that something had to be done to counter the speed and firepower added by fighter planes since the original B-17 had been designed. RAF Bomber Command decided against more heavy bomber daylight raids and pushed production of Stirlings with improved Halifax and Lancaster types, while in the future, RAF B-17s would be used by the Coastal Command.
America’s APWD/l war plan would be useless unless the bombers could be protected well-enough to penetrate to their targets, an ability not yet demonstrated by U.S. planes. Part of the answer was to replace most of the hand-held gun mounts with power-operated turrets and provide a tail gunner with a clear field of fire to the rear.
The Sperry company designed a 650-pound electric-powered dome with twin .50-caliber guns, 400 rpg, and a computer sight. Located behind the pilots’ seats, it swung 360 degrees around and 85 degrees up. Another pair of guns in a Sperry belly turret was remote-controlled from a periscope sight by a prone gunner. These turrets armed the B-17E, ordered August 30, 1940, and first flown September 5, 1941, about four months behind schedule.
Another pair of .50-caliber guns, aimed with a simple bar sight, was provided in a tail emplacement, with a narrow 60-degree cone of fire. A .50-caliber gun at each squared waist opening was hand-operated, as was the .30-caliber gun fired from sockets in the nose enclosure. Since power plants were the same as on the previous Fortress models, the increased weight and drag of protruding turrets reduced the speed, although its ability to defend itself was greatly improved. Distinguishing feature of this and all succeeding Fortress models was a large dorsal fin and wider stabilizer.
As early as December 1940, the original belly turret was seen as unsatisfactory and, after the first 112 B-17Es, was replaced in January 1942 by an 850-pound Sperry ball turret with the gunner curled up inside. But the weakness of the protection from frontal attacks was not recognized until after heavy combat losses.
The B-17E arrived just as America entered the war. Forty-two were delivered by November 30, 1941, mostly to the 7th Bomb Group, with 60 more B-17Es in December, and the last of 512 by May 28, 1942.
In 1941, there were 13 heavy bomber groups, but they were far below the plane strength planned. Only some 150 B-17s were on hand December 1, 1941, including older models, together with some B-18s for training. First priority was given to the groups deployed overseas. Twenty-one B-17Ds had been flown to Hawaii in May 1941, and the rest joined older models in the 7th and l9th Bomb Groups.