B-17 Comparson

Recently I have witnessed some total garbage written on the web about just how good some perceived the Boeing B-17 to be. I thought it time to drag out my analysis I used in my B-17 book for Pen & Sword...

Assessing the worth of a bomber aircraft by comparison with its contemporaries is not easy, for different operating parameters, along with the fast pace of change, especially during the war years, makes any form of correlation particularly difficult.

            Different national requirements and varying operational methods of achieving the desired goal resulted in great variation in bomber design. Weapons or stores carried - ‘size’ - became the yardstick and bombers were classified into light, medium, heavy and very heavy categories. However, tactical needs brought about different roles and design developments also blurred these basic classifications.

            The Model 299 B-17 was originally designed as a long-range maritime reconnaissance bomber of medium capacity during a period when the US government was actively pursuing an isolationist policy and when any form of military expenditure was only acceptable if it was for defence purposes.

            With a change of administration, and faced with the expansionist policies of Germany and Japan, the B-17 became the prime aircraft design around which the USAAC's doctrine of daylight precision bombing was developed.

            A key figure in this was Harold Lee George. An American aviation pioneer and an outspoken proponent of the industrial web theory, George taught at the Air Corps Tactical School (ACTS) and through his teachings, influenced a significant group of airmen passing through it - who were to have powerful influences during and after World War Two. He has been described as the leader of the so-called ‘Bomber Mafia’, a group of men who advocated an independent military arm composed of heavy bombers.

            George studied aeronautics at Princeton University and learned to fly at Love Field, Texas, receiving his wings on 29 March 1918. He went to France that September with an initial assignment to the 7th Aviation Instruction Center at Clermont. Two months later he was posted to the Meuse-Argonne front, piloting a bomber with the 163rd Bomb Squadron, 2nd Day Bombardment Group. In the one week that it saw action, the 163rd flew 69 sorties. George observed that massed bombers, flying in formation, swamped enemy defences and so reduced the attacker's casualties.

      In France, George met William ‘Billy’ Mitchell and became convinced that Mitchell's vision of an independent Air Force was the best future direction for the American military.

    After the war, George was assigned to the 49th Bombardment Squadron at Kelly Field, Texas, where he was promoted to First Lieutenant in April 1921. He next served with the 14th Bombardment Squadron at Langley Field, Virginia, and with the Aberdeen Proving Ground, Maryland. From 1921 to 1923, George assisted Mitchell in his bombing demonstration against old battleships, and helped develop air-to-ship tactics. In August 1925, George went to Washington as chief of the Bombardment Section in the United States Army Air Corps Operations Division.

            In July 1929, George was ordered to Hawaii for two years with the 5th Composite Group at Luke Field serving Pearl Harbor. In September 1931, he went to Maxwell Field, Alabama, to study at the ACTS where he helped refine the precision daylight bomber doctrine taught there. Following graduation, George became an instructor at ACTS, teaching air tactics and precision bombing doctrine and became de facto leader of the ‘Bomber Mafia’. With Haywood S Hansell, Laurence S Kuter and Donald Wilson, George researched, debated and finally codified what the men believed would be a war-winning strategy that Wilson had termed as the ‘industrial web theory’. This was a military concept which stated that an enemy's industrial power could be attacked at nodes of vulnerability, and thus the enemy's ability to wage a lengthy war could be severely limited, as well as bring down his morale - his will to resist.

            In 1934, George was made director of the Department of Air Tactics and Strategy, and vigorously promoted the doctrine of precision bombing. It was through his directorship of ACTS, that George became known as the unofficial leader of the men in the USAAC who closed ranks and pushed exclusively toward the concept of daylight precision bombing as a strategic, war-winning doctrine using massed air fleets of heavy bombers commanded independently of naval or ground warfare needs. This concept was to influence more than a generation of thinkers within the USAAC, USAAF and even the USAF and, apart from a period when the USAAC adopted the RAF-style area bombing tactics using B-29s over Japan that cumulated in the dropping of the two atomic bombs in August 1945, continued right through to the 1970s and Linebacker II missions over Vietnam. It was also to strongly influence the designers and manufacturers of bomber aircraft.

            George was promoted to major in July 1936. He graduated from the Command and General Staff School at Fort Leavenworth, Kansas, the following year and returned to Langley as commanding officer of the General Headquarters (GHQ) Air Corps 96th Bombardment Squadron. George flew to South America as a part of a series of USAAC goodwill flights in February 1938 and November 1939. In 1940, George took command of the 2nd Bombardment Group.

            With intelligence gained from the early months of air fighting in Europe, the B-17 was re-designed to improve its defensive firepower and to give it improved high altitude stability to provide a better bomb sighting platform. It received a further re-design following the experiences of the RAF operating a small number of B-17Cs in actual, not simulated, combat.

            From concept and through the re-designs, the B-17 was tailored to operate in the sub-stratosphere altitudes of between 20,000 to 30,000 ft, and in daylight. The effective turbo-supercharging of engines, an excellent crew oxygen supply system and an accurate high altitude bombsight - without doubt for which extreme preference was given to the Norden version - were crucial elements in this development. The thinking behind this was that the higher the altitude, the less effective anti-aircraft artillery would be against the bomber, and any intercepting fighters would suffer a heavy drain on fuel in climbing to reach these heights, severely limiting their endurance.

            Bombardiers liked to boast that with the Norden bombsight they could drop a bomb into a pickle barrel from 20,000 feet. When asked if that was true, inventor Carl Norden is supposed to have responded, ‘Which pickle would you like to hit?’ Norden’s President, Theordore H Barth is said to have postulated ‘We do not regard a fifteen foot square...as being a 'very difficult' target to hit from an altitude of 30,000 feet, provided the new Army M-4 bombsight together with Stabilized Bombing Approach Equipment is used’.

            Postwar evaluation of this battle between Norden and Sperry showed that precision high-altitude bombing was much less effective than believed during the war. Although the visual bombsights worked, the generally poor weather over Europe interfered with their success. By the end of the war, both radar-guided and television guided bombs were under development.

            Although based on technology from the early part of the century, the Norden sight was important because of its popularity and its role as a morale booster and ultimately because it did equip three quarters of US bombers. Although less well known, the Sperry sight was based on later technology that ultimately facilitated the development of avionics for all-weather flying. Its legacy lasts to this day, in electronic autopilots and in the gyro-syn compass that is still the standard heading reference on most commercial and military aircraft.

            How much of what has been quoted about the Norden was factual, and just how much was hyperbole depended much on where the aircraft was being flown. In the clear, peaceful skies over the deserts of the south-western USA performance figures were considerably different to the cold, wet combat-filled air of northern Europe.

B-17 vs B-24

The only operational bomber that stands a direct comparison to the B-17 was its running mate in the strategic bombing campaign over Europe, the Consolidated B-24 Liberator. A later design by four years, the Liberator understandably embodied some of the new developments in aircraft engineering and equipment that was not available when the B-17 first appeared.

            Inevitably the virtues and vices of the two aircraft have been endlessly discussed over the ensuing years, but nowhere more avidly than among those who flew or serviced them. Basically the two bombers had similar specifications and performances, being designed and developed for the same purpose. On the other hand each had distinctive handling qualities and operational characteristics. For the men who entrusted their lives to one or the other there was no debate: if you flew a ‘Fort’ then the ‘Lib’ was the inferior aircraft, and vice versa. Reason just did not enter into it. Verbal antagonism was common. To the Fortress men the B-17 was the 'Queen of the Sky' and the B-24 '...that Banana Boat'. To the Liberator adherents the Fort was 'that heavy bombardment training plane' while their own charge was 'a real man's ship'.

            Many of the derogatory remarks were aimed at the B-24; ‘..it having been designed as a flying boat but leaked so badly they decided to put wheels on it instead’. Then there was ‘...the B-24 was the packing case they sent the B-17 over in'.

            A more truthful jibe, supposedly originating from a B-17 Group Commander: 'Who needs escorts when there are B-24s around?' - a statement referring to the lower altitude at which B-24s were forced to operate, thus making them inviting targets for both flak and fighters.

            This battle was known to be expressed in more dangerous ways. Performing some aerial manoeuvre for which a B-17 or B-24 was not designed in the presence of operators of the other type was a not infrequent occurrence, although liable to get the rogue pilot grounded if witnessed by authority. Reports exist of a B-17 formation ploughing across an overcast at 150 mph during a training mission who were amazed to see an old B-24 go sailing past at apparently twice their speed with a pair of naked backsides framed in the waist window in a vulgar gesture. The Liberator pilot apparently attained this turn of speed in a dive from higher altitude.

            Another story relates to what could be called the ultimate in B-17 one-upmanship,  a prank performed by a pilot assigned to the ‘Aphrodite’ unit at Fersfield. Gremlin Gus II as already described was sometimes called ‘The Roadster’ and this unique machine caused considerable interest wherever it appeared. Being some three tons lighter than an empty combat Fortress due to its gutted state, Gremlin Gus II had a considerable turn of speed. A Liberator could normally out-pace a Fortress so that every B-24 pilot knew he was unlikely to be overtaken by the Boeing. The operators of Gremlin Gus II delighted in exploiting this situation. A story is told about how Major Hayes of the Aphrodite unit would allegedly stalk a B-24 formation, amble alongside and then smartly advance all throttles to full power, whereupon Gremlin Gus II would speed by. As the head of the formation was passed, Hayes would stand up in the open cockpit and salute!

            What is clear from the facts and figures is that the B-17 was more suited to the type of operations undertaken by the USAAF, primarily because it had better high altitude performance. A loaded B-17G was a relatively stable aircraft, even at 25,000 ft, and was not difficult to control at 30,000 ft. A fully loaded B-24J required constant pilot attention to maintain position in formation at 20,000 ft, at 25,000 ft it was floundering around the sky.

            The characteristics of the B-24's high aspect ratio wing, the so-called ‘Davis’ wing, named after designer David R Davis, were not suited for flight in thin air while supporting a heavy load. Above 18,000 ft the B-24 became progressively demanding of the pilot on the controls as altitude increased, while the Fortress presented no detrimental change until over 30,000 ft. However, at lower altitude most pilots with experience of both bombers considered the B-24 easier to handle.

            Both types of aircraft had turbo-supercharged engines but the B-24 used the Pratt & Whitney 1830 whereas the B-17 had the longer stroked Wright 1820. The 1830 demonstrated better reliability and did not use, or disgorge, oil to the same extent as the Wright. The take-off horsepower rating of 1,200 was the same for the two makes so the B-24's slightly better performance can be attributed to cleaner aerodynamic design.

            Both the B-17 and the B-24 had bomb bays the full depth of the fuselage. The B-24's bay was divided into a front and rear section which together provided almost double the space of that in the B-17. However, the design of the bay and racks limited the largest size of individual bomb to 2,000 lb, of which the Fortress could carry two and the Liberator four. With combinations of smaller bombs the load could be substantially increased, particularly with the slim 1,600 lb armour piercing bombs, of which the B-17 could accommodate six totalling 9,600 lb and the B-24 eight with a total of 12,800 lb.

            If the under-wing racks were used then heavier bombs could be lifted, but these very heavy loads brought flight stability problems. In practice, tactical considerations - of range and altitude - were the influencing factors and average bomb loads for the B-17 and B-24 in the USAAF high altitude daylight operations were 5,000 lb and 6,000 lb respectively. In operations over Europe, to reach more distant targets, loads were often l,000 lb less than the average. The heaviest operational load known lifted by a B-17 was two 4,500 lb Disney rocket bombs on under-wing racks and this demanded caution at the flight controls. The racks were used to supplement bomb bay loads when attacking short range targets, but the effect upon high altitude climb through the increased fuel consumption at high engine temperatures limited their use.

    At similar loadings and at the same altitude the maximum speeds of the B-17G and the B-24J were much alike, 280 mph and 290 mph at 25,000 ft. The difference in combat cruise speed was more marked; 208 mph true airspeed for the B-17G as against 220 mph for the B-24J at 20,000 ft, due to the slightly higher power settings required by the B-24. This difference in airspeed was enough for it to be undesirable to fly the two types in adjacent formations.

            When it came to range with the same amount of fuel and the same altitude, the B-24 could achieve up to 100 miles more than the B-17. Both aircraft had provision for additional fuel tanks in the bomb bay which would add an additional 1,000 miles to range. The larger bomb bay of the B-24 still allowed for a reasonable bomb load, whereas in the B-17 this was seriously curtailed. It was for this reason that the B-24 was the preferred type for maritime patrols or in the Pacific war zones, where much greater distances than in Europe had to be flown on combat missions.

            Range considerations were the principal reason for the B-24 replacing B-17s in the Pacific. In Europe the reverse was the case. The Fortress's better high altitude behaviour found it the more favoured type with USAAF commanders. The B-17's excellent flight characteristics, the foremost being directional stability with little requirement for trim, made it far more suited to survive damage than the B-24. Several Fortresses were landed successfully with complete tail stabilisers shot off and major damage to wings. B-24s were in general less able to keep flying with comparable damage to flight surfaces.

B-17 vs the Soviets

The Russians were mainly interested in air support for their ground forces, although a few four-engined bombers were produced. One was the Petlyakov Pe-8, which was originally known by the Soviet bomber designation T-7 until that system was dropped in favour of acknowledging the leader of the design team responsible for an aircraft. Most of the total of 79 Pe-8s reputed to have been completed were on hand before the German invasion of the USSR in August 1941, but the type remained in service until the end of hostilities. During the war years many Pe-8s were extensively modified and re-engined, once with diesels to enable these bombers to attack Berlin.

            In comparison with the B-17G, the Pe-8 was a slightly larger and more powerful aircraft. An auxiliary engine in the fuselage provided supercharging that enabled the Pe-8 to be operated at between 20,000ft and 25,000ft. At this altitude its maximum speed was some 20 mph below the B-17G's. Maximum range with a 4,408 lb bomb load was 2,900 miles at a speed of 174 mph with fuel overload amounting to a massive 4,120 US gallons. Bomb load could be doubled but this severely curtailed range and altitude performance. The B-17 could only equal or better this range by using bomb bay fuel tanks which then reduced its payload to 2,000 lb.

            The armament of the Pe-8 featured a 20mm cannon in the nose, tail and dorsal turrets, all manually manipulated, and a single machine gun in manned emplacements at the rear of each engine nacelle. Although heavier weapons were employed, the Pe-8 was less well defended than the B-17, particularly as the US type's power turrets were far superior in operation to those on the Russian aircraft. The Pe-8, like the other non-US bombers, operated chiefly at night with a view to improving its chances of survival in hostile airspace.

B-17 vs the Axis

 The Luftwaffe was created to support land forces and was in reality a tactical air arm. German interest in long range heavy bombers was limited and only one model in this classification entered service, but others were under design and development before the end of hostilities. Luftwaffe bombers of the early war years were in the twin-engined light or medium classification. There were no plans for strategic bombing forces prior to hostilities, air power being centred on support of army and navy operations. The Luftwaffe's sole heavy bomber to go into service was the Heinkel He. 177 Greif. Of similar dimensions to the B-17 and the other Allied four-engined bombers, it had the novel feature of using two coupled liquid cooled engines in each nacelle, thus driving a single large propeller on each wing in order to minimise drag. This proved to be the weak feature of the design, as the He.177 was plagued with recurrent engine overheating problems that took the best part of three years to resolve.

            In comparison with the B-17G, a much older design, the He.177A had a lower operational altitude — around 15,000 ft — against the B-17's 25,000 ft. The service ceiling of the Heinkel was 25,250 ft against the Fortress's 35,600 ft. The He.177's maximum speed was 314 mph at 20,000ft, some 25 mph higher than the B-17G at the same altitude, chiefly due to far more powerful engines. The Heinkel could lift ordnance loads as heavy as the British bombers, but much of this had to be carried externally. The normal operational load was only 4,480lb although this corresponded with that of the Fortress on very long range flights; but even so it was able to haul this load some 500 miles further than the Fortress could at 20,000ft. The He.177 flew at night during its limited bomber operations over Britain and the USSR but was also used in a long-range anti-shipping role. The defensive armament was good, albeit nowhere as extensive as the B-17Gs, but on some versions it included two 20mm cannon.

            The Japanese, like their Axis partners, concentrated on employing air power in support of army and navy operations. A solitary four-engine heavy bomber design was produced and first flown in 1936, but never reached quantity production. They did not produce a modern four-engined heavy bomber until 1944 and this type never entered service.

            The only other four-engined heavy bomber to be employed operationally by the Axis air arms was the Italian Piaggio P.108B. First flown in November 1939, this type was of similar configuration to the early B-17 and is said to have had excellent handling characteristics. However, the aircraft proved to be mechanically unreliable and production was curtailed after only 26 had been completed. Nevertheless, during 1942 and 1943 the only unit of the Italian Air Force - the Regia Aeronautica - equipped with the P.108B did undertake 29 operational sorties. During these operations five of the bombers were shot down and three lost through mechanical failure or accident.

            Compared with the B-17G, the P.108B had a much lower operational altitude range, 15,000ft being the optimum with a service ceiling of 20,000ft. Its top speed was also some 20 mph slower than that of the B-17G at 15,000ft despite higher rated engines. With a normal bomb load of 2,2051b the Piaggio's range was approximately the same as the Fortress's. The Piaggio had a greater maximum internal load capacity amounting to 7,716 lb for short range flight but engine difficulties precluded such heavy lifts on operations. An advanced feature of the P.108B was the two remote controlled twin machine gun barbettes mounted at the rear of each outboard engine nacelle and sighted from stations on the fuselage. A single machine gun in a retractable 'dustbin' type turret provided underside defence but this was both cumbersome and considered ineffective. Overall the seven or eight machine gun defensive armament was vastly inferior to the B-17G's but, in fairness, this bomber was more the contemporary of the B-17F model than the G, even though in the matter of comparison the same judgements apply.

B-17 vs British designs

In contrast to the USAAF, the heavy bombers developed for the Royal Air Force were expected to operate mainly under cover of darkness and at much lower altitudes. When comparing the B-17 with the three major British four-engined bombers, there are two major differences - the amount of defensive armamant carried and the maximum bomb loads.

            The Short Stirling, earliest of the British designs, could accommodate and lift 14,000 lb, the Handley Page Halifax 13,000 lb, and the Avro Lancaster 14,000 lb in standard, unmodified form. The more extensive bomb bays in the British aircraft, in contrast to the B-17 and B-24, only occupied the fuselage area below the wing spar and were not encumbered by walkways. This allowed the carriage of more bombs and, in the case of the Halifax and Lancaster, larger bombs, with single 4,000 lb bombs being dropped regularly by Lancasters in amongst other munitions carried. Much larger single bombs were also carried and modified Lancasters were quite capable of carrying and dropping 22,000 lb deep penetration missiles.

            The normal maximum loads of the British bombers could only be carried some 750 miles at operational altitude by the Stirling, 1,000 miles by the Halifax and 1,500 miles by the Lancaster. Loads were substantially reduced for long ranges but Lancasters and Halifaxes regularly hauled 10,000 to 12,000 lb loads to the Ruhr and 8,000 lb loads to Berlin.

            Unlike the USAAF day bombers, RAF heavies operating at night did not circle to gain altitude before setting course to penetrate enemy airspace. Normally the British heavies made their ascent during the run up to the enemy coast. The Stirling could not operate with a combat load at much above 15,000ft and the Halifax Mks I and II above 18,000ft. The radial engined Halifax Mk II did operate successfully at 20,000ft, which was also the optimum level for Lancaster sorties. The B-17G had better range than the Stirling and Halifax and marginally better than the Lancaster while flying at similar altitudes. All the British bombers had, on average, double the pay load for similar ranges but the Lancaster's larger fuel load allowed it, even with a 10,000 lb load, to match the B-17 on radius of action.

            In the matter of armament differences the B-17G had far superior firepower to the British bombers: thirteen .50in calibre machine guns to the usual eight .303in machine guns in three power turrets of British bombers. Moreover, the US .50 weapon had a higher muzzle velocity and much more destructive power than the rifle calibre weapons which defended the RAF bombers. To improve matters Lancasters of one Bomber Command Group had two .50s as tail turret armament during the final months of hostilities. The British bombers did not have underside defences and were very vulnerable to attack from that quarter, albeit that in any event, an approach from below by an interceptor could rarely be seen at night until it was too late. In fact, the difficulty of being alerted to an enemy fighter's presence in any quarter during the times of darkness was the greatest problem of bomber defence. Given the technology available at the time, there was almost a fatalistic inevitability amongst RAF bomber aircrews that not much could be done.

            Instead the RAF turned to different tactics - by making use of the small, fast, highly maneouverable De Havilland Mosquito twin-engined night fighter flying within the bomber stream to act as ‘bait’ to German night-fighters. When spotted on the tail warning radar in the Mosquito, the pilot would quickly loop around, picking up the German machine on his main radar and then bring his four 20 mm cannon to bear on the rapidly closing target.

            The wooden composite De Havilland Mosquito - originally designed as an unarmed high-speed bomber but also produced in Photo-Reconnaissance, Fighter and Figher-Bomber variants - sacrificed the weight of excessive armament for the safety gained from performance could uplift the same bombload internally as that of a B-17. The two-man crew could also theoretically make two trips to Berlin from England in the same time it took a 10-man B-17 to make one!

            Fortresses were experimentally employed on night operations, but the limitations on bomb load made such sorties uneconomical. By daylight the precision that could be achieved and the mass formation drops employed were regarded as the proven means of using the type successfully.

            Lancasters and Halifaxes frequently took part in daylight bombing of Ruhr targets during the final year of the war, by which time the Luftwaffe was in demise and fighter escort was provided to and from the target. Formations flown were much looser than those of the USAAF and target sighting was performed from individual aircraft. Attack altitudes - 15,000 ft to 18,000 ft - were generally lower than those of the US heavies. Each of the British bombers delivered a more destructive load but post mission reconnaissance showed that this was more scattered than the formation drops of the B-17s and the B-24s. However, the USAAF did use exactly the same area bombing techniques over Japan.

The B-17 munitons

When one tries to compare the B-17 with other aircraft, one needs to consider the munitions available for use. As the B-17 was used more in the ETO than in any other theatre then this area is a good one to study.

            Munitions fell into a number of categories: General Purpose (GP) High Explosive (HE) bombs, Incendiary bombs, and then a whole swathe of what could be called ‘Special Use’ bombs.

            The glide bombs, the GB-1 and GB-4s, are covered elsewhere, as are the Disney rocket weapons. The B-17 could carry chemical weapons, by far the worst being the poison gas bombs, which were in two types - the 400 lb mustard gas bomb codenamed Flying Cow and the 500 lb phosgene bomb. In 1942 several thousand M47A2 HS unfilled incendiary bombs were set aside for use with mustard gas and held ready in muntion stores. Storage levels appear to have been 40,000 M47 100 lb mustard bombs and 50,000 phosgene bombs. There is no record of any being used.

            Another chemical weapon became available to the USAAF in the second half of 1944, when a refined petroleum jelly known as napalm became available. Handled in bulk it was intended for filling as required. Tested in various containers, the preferred type was the paper composition fighter fuel tank of 108 US gallon capacity. Known as Class C-Fire Bombs, napalm tanks were used on a few special missions where blanket fire cover was required, notably against German strong-points on the French coast in April 1945. Usually four napalm tanks were carried in a B-17; small incendiary igniter units were fixed to each tank.

            Fragmentation bombs, which were basically anti-personnel munitions, were used mostly in tactical attacks in support of ground forces. The 20 lb M41 was common to both the M1 and M1A1 - which were differing in attachment arrangement - clusters of 120 lb and the M26 clusters of 500 lb. The M1A1 was employed extensively in heavy bomber loads. To enable fragmentation bombs to be used in conjunction with the Norden sight it was necessary for special computation tables to be used as the maximum trail angle of the sight was not great enough for the light bombs.

            When they began operations, the 8th Air Force were using the old type of GP bombs of 100, 300, 500 and 1000 lb size ratings. It was not long before supplies of these were exhausted and the new AN (Army/Navy) bombs were used, these being categorised as the M30/100 lb, M31/300 lb, M43/500 lb, M44/1000 lb and M34/2000 lb.

            In general terms, the 500, 1000 and 2000 lb muntions were used against industrial targets while the smaller sizes were used against airfields. In practice, little use was made of the M30s. Likewise, use of 1000 and 2000 lb GP bombs were found to be of little use against the submarine pens themselves, for they either just bounced off or barely chipped the concrete, although significant damage was done to adjacent structures.

            At one time the 8th considered operating in two waves, the first dropping 1600 lb US Navy Mk 1 armour-piercing bombs which were expected to crack the concrete, and then to follow up with a second wave dropping 2000 lb GPs to blast through. Two attempts to achieve this were made at Lorient, but the only successful drop, on 30 December 1942, gave disappointing results, basically because it was not possible to obtain successive strikes with the two types of bombs.

            An intelligence report on the December 1942 Lille mission showed that 30% of bombs dropped failed to detonate. There were indications that the mechanical arming mechanisms of the fuses had frozen. Trials showed that things could be improved if the bombs were not fused until shortly before take-off, thus reducing the time the fuses were exposed to damp. Even so, a high percentage of detonation failures persisted, even in warmer weather. British fuses were adapted for American bombs and in the spring of 1943 US chemical action long delay fuses were received for service tests. These had an anti-withdrawal device to prevent defusing by the enemy. Fortunately a method was devised in the UK for removing these fuses safely, sometimes necessary with aircraft that crashed on take-off.            

            A new range of GP bombs became available late in 1943, the M57/250 lb replaced the M31, then there were the M64/500 lb, M65/1000 lb and M.66/2000 lb. These munitions made up the greater part of the tonnage delivered by the 8th during the final year of operations. A small number of M56/4000 lb bombs were received in 1944 but could not be carried internally by either B-17 or B-24. Experiments to use them on under-wing racks of B-17s were not successful and no record has been discovered to suggest that M56s were delivered on combat missions. While the large 1000 and 2000 lb bombs continued to be used on industrial targets, by January 1945 analysts were recommending 250 lb GP to be used against synthetic oil plants, refineries and storage tanks as well as against ammunition supply and dump targets. The 100 lb GP bomb was advised for attacking marshalling yards and for cratering airfields.

            The first incendiary bombs used by the 8th Air Force were British, either 250 lb or 500 lb. Both were filled with a rubber/gasoline mixture. It was not long before the American M50A1 4 lb magnesium incendiary in 100 lb clusters became available for use, along with a 500 lb cluster version and an 100 lb M47 type. However, these clusters proved unsatisfactory as they opened quickly, causing excessive dispersion, some aircraft in the formation being damaged by clustering material, so use was suspended. The 8th then began trial missions with the M47, and discovered that a full load only amounted to 24 due to the limited number of shackle points in a B-17 bomb-bay. It was not until July 1943 that a successful method of clustering M47s together was achieved. Wire cables with snap hooks were used to hold three or four bombs together, but in such a way that after release there was separation, the cables being carried down with one bomb. This not only allowed three or four M47s to be shackled to one station in the bomb-bay, increasing the total load to 42, but also avoided damage to other aircraft. This ‘shackling’ became standard operating proceedure for use with various other small bombs.

            Other incendiary munitions were the M52, a 2 lb magnesium type, and the M69, which weighed 6 lb and was filled with petroleum gel. The M69 was later packed in the M12 cluster. In January 1944 8th Air Force started to use the 500 lb M17 aimable cluster containing 110 M50A1s with better ballistics than the earlier M11 cluster; it had a primacord release that could be set to give the desired scatter. A larger petroleum gel filled bomb, the M76/500 lb, was introduced in 1944 and used with some effect during the rest of the 8th's campaign.

            The M50A1 which made up magnesium incendiary clusters had a hexagonal, cored magnesium alloy body with-hollow steel sheet fins containing thermite with an igniting charge and fuse. On ignition, the M50 burned for six to eight minutes at a temperature of 2300 degrees F. The preferred jellied-oil incendiary, the M47A2, had a thin-walled steel cylindrical body weighing 26 lb empty and on impact gave a 120 feet fire spread.

            All of this gave the B-17 a wide range of small-to-medium munitions that could be carried.

The failure of the industrial web theory.

American bombing leaders maintained that precision attacks were being carried out by B-17s and B-24s, but in early 1944 poor weather over Europe prevented visual sighting, and bombs were dropped indiscriminately by inaccurate radar methods through cloud cover, resulting in general population destruction. By September 1944, all pretence to precision was abandoned when General Dwight D Eisenhower ordered the area bombing of Berlin. By that time, bombing was not so much strategic as it was tactical, to soften Germany for invasion by ground troops. Thousand-bomber raids were not able to diminish industrial production of war materiel in time to prevent invasion. When arms production in Germany finally faltered in the third quarter of 1944, only 30% of the total of eventual bomb tonnage had been dropped on the country - this was after the French-German border had been reached and the war on the ground had seen its decisive breakthrough. It must be said that Germany was conquered by invasion; it did not surrender as a result of bombing. The morale of the enemy was not significantly affected; no population that was bombed in World War Two lost their will to resist, and it was the Emperor, not the people, who decided Japan must surrender.

The problem with the B-17...

The ‘designed in’ problem with the B-17 was the bomb-bay. From the outset the B-17 was a medium bomber and, because of the way the bomb-bay was designed and positioned, there was absolutely nothing that could be done to allow the internal carriage of the larger weaponry as it became available or was required.

            The B-17 bomb-bay was eight foot nine inches long by seven feet wide, but this had to be divided in two down its length and then subtract the nine inch wide walkway that formed part of the keel of the aircraft. This gives two ‘holes’ 105 inches long by 37.5 inches wide.

            Much has been made by those promulgating the abilities of the B-17 about the fact that there were 42 internal ‘positions’ on four racks that bombs could be hung on. This was certainly true, and indeed there were also two external racks as well. However, they also convienently forget to mention that depending on the size of the bombs carried and the distance from the operating airfield  to the target, virtually all of these positions were completely unusable mainly because of whatever was hung on them had to be ‘stacked’ one above the other and they had to pass through two ‘holes’ filled in by the bomb bay doors. Indeed, the pair of ferry fuel tanks were conformal in shape in order to maximise the possible uplift. Everything had to be fitted into two areas deliniated by the front and rear bulkheads of the bomb bay, the sides of the fuselage and the edges of the walkway. No matter what the volume of the bomb bay, this simple area restriction gave two apertures each slightly over twenty nine square feet in area for bombs to drop through, thus limiting the aircraft weaponry uplift.           

            The British Avro Lancaster, on the other hand, did not have that problem. The bomb bay in this machine was thirty three feet six inches long and sixty-two inches wide, with three ‘racks’ running the entire length. That is slightly over one hundred and seventy three square feet of completely unobstructed, usable bomb bay. If a bomb could fit in that area, it could be carried - and if it could not fit inside the bomb-bay with the doors closed, there was no problem - either bulge the doors or remove them all together!

            In the immediate post-war years a number of studies by the Allies were conducted, to coldly calculate losses and the so-called ‘efficiency’ of different aircraft designs.

            Overall, it was stated that as the ‘ultimate’ B-17, the B-17G had a superior high-altitude performance to all other Allied and Axis bombers. In maximum speed the only notably faster bomber was the He 177. In tactical speeds the Fortress was similar to its contemporaries except when flying in formation where uniformity demanded lower power settings and therefore lower speed. The B-17G's range was better than that of the British heavies, equal to the Piaggio but less than the Pe-8 and the He177 with similar bomb loads. In the matter of maximum loads it was at the bottom of the scale, particularly  in comparison with the British bombers. In the case of defensive armament the B-17 justified the name Fortress, for in number of guns, calibre and effectiveness it was the best armed, with the B-24 running a close second.

            If cautiously loaded, the B-17G had no really undesirable flight characteristics and was a pilot-forgiving aircraft, easy to fly. While it is extremely doubtful if any one pilot had experience of all the types reviewed it appears that, with the exception of the Lancaster and Liberator, the other types left something to be desired in mechanical ability or operation. Opinions from those who have flown Lancaster, Liberator and Fortress single out the last named as the least demanding, even at low and medium altitudes.

            Of all the ‘efficiency studies’ located, one is of particular interest, for it broke the figures down in a similar manner to how airlines of today cross-compare their statistics in load-factors and seat cost per mile to generate a common denominator. However, the originators of the study were somewhat selective in their choice of aircraft to compare.

            The first calculation it used was to divide the bombload by the number of crew on board - this gives a figure that describes the destructive weight uplifted per man on board the machine. The second was to state a nominal mission distance, in this case 600 miles, 1200 miles round trip, which happened to be an average distance from the UK to Berlin and to work out an average point-to-point time taken by each aircraft to cover that distance at the quoted combat speed.

            The original study compared the B-17G to the Stirling, Halifax and Lancaster. Missing from the table was the Lancaster (Special) and the Mosquito, which was considered a light bomber anyway. It also did not take into account the different styles of operation between the RAF and USAAF in that the RAF did not require formation assembly, which could add at least an hour to the time. Both of these omissions create a somewhat slewed view. Today, inserting those two aircraft into the table gives a far better perspective.

In conclusion...

To try to make a comparison and then to say that one design is ‘better’ than another is too simplistic and just exhibits what today would be termed ‘blind brand loyalty’. Each design served, and in many ways met and exceeded, the purpose of its creation. Sometimes the urgent needs of combat - or political expediency - meant that this was outside the design parameters. This worked at times, failed at others, and in this the B-17 was no different than all the others.

            The passing of time and a number of over-active publicity machines have meant that many legends and myths have grown up surrounding both the B-17 and the Norden bombsight. Does the ‘Flying Fortress’ deserve it? That is for the individual to decide. Was it fit for purpose? Undoubtedly.