Riposte
Many German combat aircraft in service at the beginning of WWII were “second generation” designs, in the sense that they often had been re-engined, and their airframes substantially modified, in comparison with their original service versions. That included the Bf 109E fighter, but also the He 111H and Do 17Z bombers. In contrast, modern allied combat aircraft were often just entering service. Several British fighters and bombers were “Mk.I” versions, and that might well mean that they had more remaining development potential, but it also implied that they had less combat experience integrated into them. Often only small numbers of these modern aircraft were available.
This situation was at its most stark in France. As mentioned before, the Plan V of 1938 had set modest goals for the production of modern medium bombers. French industry again under-delivered, and on 1 April 1939 the air force had received 877 aircraft instead of the planned 985. This particularly affected the modern LeO 451 and Amiot 350 medium bombers, of which the air force had received none in July 1939, although it had received 927 new aircraft of other types. Thus, while in August 1939 the air force considered that 938 out of its 1511 fighters could be considered modern, it possessed a grand total of 20 modern bombers: 15 Potez 633 light bombers, 4 LeO 451 medium bombers, and one Loire-Nieuport LN 411 dive bomber. By September 1st, the number of LeO 451s rolled out from the factories had increased to 22, of which 10 had been formally accepted by the air force. Production of this type was hoped to increase to 90 per month by the end of the year and 200 per month by the summer of 1941 (later adjusted to 150). By that time the Amiot 350 was also expected to be built at a rate of 123 per month (later adjusted to about 50). To bridge the gap while production was accelerated, a batch of American Douglas DB7 bombers was ordered.
The slow start of production resulted in a situation that was later considered scandalous, but was in fact normal. By May 1940 a significant number of these modern bombers existed, but they were at depots, awaiting the training of crews, the installation of equipment, or assignment to frontline units. The modern, but complex LeO 451 was a prime example of this: Of 215 aircraft built, the air force had received 106, of which 54 were available for operations. By the time of the armistice, the total of received aircraft had reached 365 – but if it was not necessarily too little, it was certainly too late. L’Armée de l’Air would end the short battle of France with, on paper, more aircraft than at the start of the fighting. But the delivery of 288 modern bombers in May and 185 in June was for all practical purposes irrelevant, as the battle was over before they could have any effect on it. We will never know what impact the LeO 451 and Amiot 350 might have had on the course of the war. The former would be put back in production for Vichy France and see very limited operational use.
France tried to fill the gaps in its inventory by purchasing American aircraft. In 1937 the US Army Air Corps formulated a requirement for a new twin-engined bomber, a dual-role aircraft, capable of both precision bombing from altitude and low-level attack missions. According to Ed Heinemann, who became chief engineer on the competing Douglas DB-7A, the specification was influenced by reports from the wars in Spain and China. It was to be a fast and relatively small aircraft, with a range of 1200 miles (1930 km) and a bomb load of 1200 lb (545 kg). The competitors were the North American NA-40, the Douglas 7A / 7B, the Martin 167, and the Stearman X-100. President Roosevelt secretly gave approval for the French purchasing commission to have a look at the prototypes. Political mayhem ensued when a member of the French commission was hospitalised and it leaked out that he had been aboard the crash-landed Douglas 7B prototype. (According to Ed Heinemann, somewhat improbably, as a stowaway!)
France decided to order both the Glenn Martin 167-F1 and -F2 (an initial order of 215, followed by 280 more) and the Douglas DB7 (an order of 100). The 167 had been designed by a team lead by James McDonnell as a small and streamlined aircraft, powered by two R-1830 radials. It was more conventional than its competitors, being a mid-wing design with a tail-dragging landing gear, while the NA40 and DB7 were high-wing designs with tricycle undercarriage. The 167 had a crew of three, the pilot, the bombardier in the nose with backup flying controls, and a radio operator who also manned the dorsal turret and ventral gun to defend the rear. After the signature of the contracts in February 1939, the French put enough money on the table to enable Martin to construct and tool up the largest aircraft factory in the USA. The first 167s were ready for delivery in September 1939, but on the outbreak of war the US Neutrality Act embargoed deliveries and it took until November before the US administration found a way around this. The first aircraft arrived in French Morocco in December. By April 1940 the initial order had been delivered, allowing the French to equip four squadrons with the “Glenn”. The Douglas DB7s arrived later, in February 1940, but this type did have substantially more redesign work done in relation to the first prototype.
A plan that was actively studied until May 1940 involved attacks by medium bombers on the Soviet oil fields in the Caucasus. Under trade agreements between Germany and the USSR signed after the Molotov-Ribbentrop pact of August 1939, the USSR was supplying about a million tons of fuel per year. The attack would have involved Martin 167 and Blenheim Mk.IV bombers based in Syria and Iraq. It is probably fortunate that it never happened. It could very much have been an event in which bombing changed the course of history!
The Anglo-French Purchasing Board were proactive customers, who requested changes such as the addition of armour protection and self-sealing fuel tanks to the 167-F3 and 167-F4. Their interest in the use of the more powerful R-2600 engine stimulated the development of the Martin 187 from the 167, while a similar change to the DB7 resulted in the excellent A-20 attack bomber. Up to June 1940 they allocated a billion dollars for the purchase of 8,500 aircraft, and their money transformed an US military aviation industry that was used to receiving only small orders. But it was a seller’s market: The French calculated that the prices they paid for US-built aircraft were 50% to 100% more expensive than their own. On the other hand, the speed with which the 167 and DB7 were built and delivered was astonishing. It still wasn’t as fast as the French had hoped, but by modern standards this is almost incomprehensible.
As for the 167F, at the time of the German attack in May 1940 the units had not been fully trained on them, but their loss rates were lower than other French bombers. It wasn’t very well defended (two 7.5mm MAC 1934 guns, one in the dorsal position and the other ventral, plus four fixed guns in the wings) but it was fast, cruising at 399 km/h with a maximum speed of 489 km/h. This was offset by a bomb load of maximum 800 kg. The crisis that developed on the ground after the German breakthrough at Sedan meant that most missions were tactical, targeting enemy troop concentrations or infrastructure such as bridges. The DB7 would see combat over France as well, from May 22 onwards. The French finally lost 40 Martin and 20 Douglas bombers in combat. Survivors were flown the French North Africa to avoid capture by the advancing Germans. Vichy would later use some in combat, notably against the British and Free French forces during their invasion of Syria. The 167s not yet received by the French were taken over by the RAF, who employed the type as the Maryland. The RAF employed 75 of the French order as the Maryland Mk.I, and 150 with more powerful engines as the Maryland Mk.II. It was an effective reconnaissance bomber in the Mediterranean theatre, but suffered from the same inconvenience of a too cramped crew accommodation as the Hampden, discussed later.
Imported bombers were very useful to the RAF but less crucial than they had been for l’Armée de l’Air. In 1936 the Air Staff had written two specifications for the bombers it needed for a future war. B.12/36 was an ambitious four-engined bomber, conceived as faster than existing bombers, with a cruising speed of 230 mph (370 km/h) and a maximum speed of 275 mph (442 km/h). The ability to carry heavy defensive armament was seen as a key advantage of a four-engined design, with four .303 guns in a tail turret, two in a ventral turret, and two in a nose turret. Primarily intended for use against land targets, B.12/36 would have to be able to carry up to 14,000 lb (6340 kg) of bombs, but no type of bomb heavier than 2000 lb (907 kg). Interestingly, the B.12/36 was supposed to carry only 2000 lb for 2000 miles (3200 km) when taking off from 500 yards of grass airfield, or 4000 lb if 700 yards were available, but much heavier loads of bombs and fuel with catapult take-off. A range of 2000 miles was considered sufficient to attack Berlin, but the ferry range was set at 3000 miles to be able to reinforce Britain’s overseas territories.
The other specification, P.13/36, was for a twin-engined medium bomber to be the backbone of the future strike force. It was to have a somewhat lighter armament than the B.12/36, with only a four-gun tail turret and a two-gun nose turret. Which of course was still a much heavier investment in defensive armament than found on bombers of other nations. The Air Staff backed down from demanding a 300 mph (482 km/h) top speed after being told that this would decrease range too much, as the 2000 miles operational and 3000 miles ferry range were seen as essential. So it accepted 275 mph. Again, the maximum load/range ability of 8000 lb for 2000 miles (3620 kg for 3200 km) was to be achieved with catapult take-off, while a 500 yard grass airfield would only permit 1000 lb (454 kg) to be carried over the same distance. The P.13/36 was to be able to carry torpedoes as well as bombs. And though the Air Staff did not specify the engines, it admitted internally that the Rolls-Royce Vulture was the only available option to meet these goals.
As a side track, it is extraordinary that the RAF seriously considered catapult-launching its future bombers. The performance advantages envisaged from this were very substantial, for example the “normal” take-off weight of the B.12/36 was expected to be 30,000 lb (13,600 kg) but the catapult-launched overload condition 55,000 lb (25,000 kg)! Of course it meant equipping every bomber base with one or more catapults that could launch a 60,000 lb (27,200 kg) aircraft at 110 mph (177 km/h), but for a while this option was considered more affordable and feasible than constructing concrete runways. (The Director of Works admitted that the Americans and Russians were doing just that, but offered the very British argument that they did not have good grass.) Bomber Command ended the discussion in 1940 by declaring that concrete runways were essential for both take-off and landing, and 2000-yard hardened runways became the standard for heavy bomber airfields.
Over time, B.12/36 would produce the Short Stirling, and P.13/36 would lead to the Handley Page Halifax and Avro Manchester, and indirectly to the Avro Lancaster. They were not the last word, as the Air Staff continued to debate the Ideal Bomber, but the 1936 specifications were the genesis of the late-war force. The new aircraft would not be available in large numbers until 1942, however. Meanwhile the RAF had to make do with what were perceived as interim aircraft, designs of various age and modernity.
The most numerous medium bomber in service at the outbreak of war had its origins in the wish of the newspaper mogul Lord Rothermere to possess a fast, twin-engined, six-seat aircraft. A desire that was not necessarily frivolous, because newspapers and their proprietors in interbellum Britain (and Japan) often stimulated technology development with prizes, and Rothermere had briefly and not very successfully held government responsibility for the aviation industry during WWI. Bristol’s designers offered him their Type 142, a small, all-metal, streamlined design inspired by the new generation of US airliners. The 142 impressed the Air Ministry, who expressed interest in evaluating it. Rothermere offered it as a gift and the Air Ministry accepted, but later insisted on paying 18,000 pounds for it, perhaps wishing to keep their distance from the owner’s political views — Rothermere had embraced fascism and was unashamedly pro-Hitler.
Bristol offered the RAF a military version of the Type 142, and the RAF wrote specification B.28/35 around this proposal. The Type 142M had a reinforced structure and more powerful Bristol Mercury VIII radial engines. The wing was moved 16 inches from low to mid-fuselage position to make room for a bomb bay. Still, the type was marked by not being originally designed as a bomber. It carried only 1000 lb and its defensive armament was relatively weak, comprising a basic dorsal turret with a Vickers K machine gun, and a fixed forward-firing Browning in the left wing. Such were the needs of the times that the RAF promptly ordered 150, to be followed by 450 more, before the first Blenheim Mk.I had even flown. The type entered service in March 1937. By the time of the Munich crisis in 1938 it equipped 16 squadrons. The aircraft was included in the first attempts at decentralised production in the “Shadow Factory” scheme, which would result in a large number of Blenheims being built by the Rootes group, and also in Canada. But at the same time as the Blenheim force grew, its vulnerability to modern monoplane fighters became more and more obvious. A speed of only 215 mph (346 km/h) with a full load of bombs and fuel was no longer enough to evade interception.
From January 1939 the RAF began to receive the Blenheim Mk.IV, conceived as a long-range version. This not only meant an increase in fuel capacity by installing tanks in the outer wings, it included a redesign of the nose to provide a much better working environment for the bombardier/navigator and the addition of a station for a wireless operator. This resulted in the replacement of the original short, blunt, and extensively glazed nose by a much longer “stepped” nose, with its decking sloped down asymmetrically to provide a better view for the pilot. Defensive armament was improved by installing two Browning .303 in a Bristol Mk.IV dorsal turret, and later two more in a Frazer-Nash FN54 mounting under the nose, firing aft. The new version was built in much larger numbers than the Mk.I (3297 versus 1134) and allowed the RAF to gradually retire the Blenheim Mk.I from Bomber Command. Some Mk.Is would have a new career in Coastal Command or Fighter Command as improvised heavy fighters and nightfighters. The final Blenheim model was the Mk.V, again with a redesigned nose and improved armament, built to a total of 902 but underpowered and unsuccessful.
The Blenheim was the most numerous RAF bomber at the outbreak of the war, with 1089 in service. It had arrived at the right time in that it allowed numerous bomber pilots to make the transition from single-engined biplane bombers to a faster, more advanced, twin-engined bomber. But the RAF quickly found it wanting in offensive and defensive capability, even if some of the very high losses suffered in 1939-1940 were due to operational inexperience rather than inherent deficiencies of the aircraft. The loss of over 200 over France was a bad sign and in any case, after the fall of France the Blenheim was functionally obsolete, as its range and bomb load were inadequate for attacks on targets in Germany. There was still a role for the Blenheim on fronts were the army was engaged, and the Blenheim would serve longer in the Middle and Far East than in the home country. The last operational Mk IVs, in August 1943, were based in India.
Another pair of medium bombers had been derived from specification B.9/32, which pre-dated the Blenheim. At the time the British Government was supportive of proposal at the Geneva Disarmament Conference to restrict the size of future bombers to 3 metric tonnes. Hence B.9/32 envisaged a relatively small twin-engined day bomber, limited to 6300 lb (2850 kg) empty weight and a 70ft (21.34 m) wing span. The RAF wanted an all-metal design, though fabric covering was allowed, and aimed for a range of 720 miles (1160 km) and a ferry range of 1250 miles (2010 km), with a maximum speed not less than 190 mph (305 km/h). The two designs that were developed to this specification and entered service were starkly different, but both amply exceeded these initial limits.
The Handley Page HP.52 Hampden was inspired by the analysis of older twin-engined bombers, notably the Boulton-Paul Sidestrand, which was characterised by a deep but narrow fuselage. In the interest of obtaining high performance, the H.P.52 was designed with a fuselage only 36 inches (91 cm) wide, though it was relatively deep. It was also a short fuselage, extended by a slender boom to carry the tailplane and twin tail fins. The efficiency of the four-man crew would be adversely affected by the cramped conditions. In theory the advantage of this configuration was that it allowed for the easy installation of dorsal, ventral and nose gun positions with a good field of fire, but in practice it was hard to design gun mounts that fit the compact space. It entirely ruled out turrets, and three plain Vickers K guns were installed, later modestly increased to two guns in the dorsal position. A single fixed Browning .303 was installed in the nose. At least the moulded perspex fittings of the production Hampden Mk.I made it considerably better looking than the prototypes. The Hampden had its strengths: Good performance, good handling characteristics, an excellent view from the cockpit, and a flexible weapons load.
The Hampden entered service in 1938. With an empty weight of 11780 lb (5335 kg) it had a normal loaded weight of 18576 lb (8415 kg), or 23500 lb (10670 kg) when operated as a torpedo-bomber. Its range of 1885 miles (3030 km) with a 2000 lb (907 kg) bomb load, or 1200 miles (1930 km) with twice that, was sufficient to reach targets in Western Germany, the North Sea coast, or later the French Atlantic coast. Its ability to carry an 18-inch Mk.XII torpedo or two 2000 lb SAP (semi-armour-piercing) bombs was useful against naval targets. That included very dangerous attacks on targets such as Brest, Cherbourg, or Wilhelmshaven, when major German fleet units were in port. For operations against targets deep in Germany the Hampden was quickly revealed to be less suitable. It could carry twice the load of a Blenheim, but its range was too short and it suffered from the same combination of weak defensive armament and a speed that was no longer sufficient to evade interception. In December 1940 it was decided that the Hampden would be used mainly at night – when the last Hampden mission against Germany was flown in September 1942, they had accomplished 464 daylight sorties, and 12,429 at night. But as a torpedo bomber, the type served on until 1943. Of a total run of 1450 production aircraft, the RAF would lose 607. In addition there were 150 Herefords, a variant on which Napier Dagger VIII air-cooled in-line engines replaced the normal Bristol Pegasus XVIII radials, but as the Dagger was unreliable, these were unsuitable for operational use.
The other aircraft designed to B.9/32 was very different. The design offered by Vickers employed the “geodetic” construction system which distributed loads through a basket-like network of light alloy members, covered with fabric. This was less efficient than the semi-monocoque structures that were adopted for the most modern aircraft, but it was strong and resilient against combat damage. The Air Ministry was sufficiently impressed by its advantages to order the Type 271, which made its first flight in June 1936. Though eventually named Wellington and considered a prototype bomber, the Type 271 was more a technology demonstrator. From it forked two designs that were quite different from it, while looking substantially similar to each other. The larger of the two, designed to specification B.1/35 for a twin-engined heavy bomber, became the not very successful Type 284 Warwick. The other, built to a refined specification for a medium bomber, was the Type 290 Wellington. Because it had been ordered even before the Type 271 flew, the Wellington Mk.I made its first flight in December 1937 and entered service in October 1938. At the outbreak of war, a small force of 169 was available.
Both the Wellington and Warwick had a clean aerodynamic form with considerable internal volume, but they were boxier than the rotund Type 271. The shape of the fuselage was influenced by the decision to install nose and tail turrets. The Wellington Mk.I had Vickers-designed nose and tail turrets with twin Browing guns, and a retractable “dustbin” turret to defend the lower quarter. It was powered by 1000 hp Bristol Pegasus XVIII engines. It was quickly followed on the production line by the Mk.IA, which had superior powered Frazer-Nash turrets in nose, tail and ventral positions, while the Mk.IC abandoned the ineffective retractable ventral turret in favour of a pair of manually operated beam guns. With that, the configuration of the Wellington bomber was essentially frozen. Improvements would be made to the bomb bay to enable the type to carry heavier bombs, and more visible at the exterior, various engines would be installed: 1145 hp Merlin X engines in the Mk.II, 1500 hp Hercules XI engines in the Mk.III, American Twin Wasp radials in the Mk.IV, and Hercules VI or XVI in the Mk.X. Of the medium bombers that Britain began the war with, the Wellington was clearly the best. Early experience demonstrated painfully that its defensive armament did not enable it to fly unescorted daylight missions without heavy losses. But it was a good night bomber, reliable, capable of absorbing combat damage, and lifting 4500 lb (2040 kg) over 1540 miles (2480 km) or 1500 lb (680 kg) over 2200 miles (3540 km). It was well suited for mass production, and with 11,461 built until October 1945, became the British bomber built in the largest numbers.
Although the Wellington remained operational as a bomber nearly until the end, flying its last bombing mission in April 1945, the introduction of the four-engined heavy bombers made it available for other missions, and the later models were built for Coastal Command, as “General Reconaissance Bomber” whose primary duty was to fly anti-submarine missions. The GR.VIII was a conversion of the Mk.IC, the Mk.XI was derived from the Mk.X, and the later Mk.XII, Mk.XIII and Mk.XIV were further optimised for their new role. Adaptations for the naval role included fittings to carry depth charges, mines, and in some cases torpedoes. To find their prey, GR models were equipped with radar, at first ASV Mk.II operating on the metric wavelengths, and later the much more effective centimetric wavelength ASV Mk.III sets. The latter was installed in a chin mount, which required the removal of the nose turret, and also meant that the radar could not look into a 40 degree wide sector to the rear. For the final approach, a powerful retractable searchlight, the “Leigh light”, was installed the aft fuselage. Versions of the Hercules were fitted that were optimised for low-altitude performance. The Wellington was not ideal as ASW platform, but the combination of modern radar and the Leigh Light was very effective. The astronomer Sir Bernard Lovell, who was closely involved with the installation of ASV Mk.III (a derivative of H2S navigation radar) in the Wellington, remembered that the initial attitude of Coastal Command was skeptic and even hostile. But its service entry in March 1943 resulted in a sharp increase of sightings of U-boats in the Bay of Biscay, forcing the Germans to change tactics and bringing about a remarkably fast reduction in shipping losses.
Besides trainer and transport versions, the Wellington also had two high-altitude bomber derivatives, the Mk.V and Mk.VI. The idea behind specification B.23/39 was that the bomber would fly over the target well out of reach of fighters or anti-aircraft guns. The Wellington was a somewhat unlikely choice for this as geodetic construction and fabric skinning made its fuselage unsuitable for pressurisation. Therefore, to enable the crew to operate at 35,000 ft (10,700 m), a cylindrical, almost submarine-like metal cylinder was inserted in the Wellington’s nose. Only 165 cm wide (tapering to a point in the nose) and 5.56 m long, it provided a miserable working environment for the crew, with little hope of escape in case of problems. Except for the tail gunner, whose position was retained because the planned remote-operated tail turret was not available. Lacking a pressure cabin, he had to make do with oxygen and an electrically heated flying suit, possibly making his position even more undesirable. The first Mk.V with Hercules radials flew in September 1940, followed by a second one. As these engines did not deliver the required performance the Mk.VI was fitted with Merlin 60 RM.6SM engines. The later Mk.VIA had Merlin 62 engines and omitted the tail turret. But it was not to be. The Mk.VI could fly at high altitude, but it took way too long to get there (87.1 minutes to reach 31,000 ft) and had poor flying characteristics. Unwisely, 64 example of the Mk.VI and Mk.VIA were completed, but after Pathfinder units rejected the type as dangerous, most were scrapped.
It is worth briefly discussing the Wellington’s less successful sibling, the Warwick. Specification B.1/35 sought an advanced twin-engined heavy bomber that could be put into production quickly. (The description “heavy” was later dropped as bigger bomber designs were prepared.) The Vickers team designed a version of their B.9/32 proposal with extensions of the central fuselage and inner wing. As the Wellington and Warwick designs matured, it was attempted to retain as much commonality between them as possible. This would work to the Warwick’s advantage in term of industrial policy, because without this factor it would have been cancelled outright in early 1939. But in a sense it also worked against it, because of the growing demand for Wellingtons. The bigger bomber also needed bigger engines, and none of the suggested options (Rolls-Royce Vulture, Napier Sabre, or Bristol Centaurus) were readily available, though a first prototype was flown with Vultures and a second with Centaurus radials. A solution was found in the American Pratt & Whitney R-2800-S1A4-G Double Wasp, and with these engines the first Warwick B Mk.I made its first flight in April 1942. But in January 1943 a combination of directional stability problems and obsolescence decided the fate of the Warwick, which would never enter service as a bomber, but was relegated to the second line as air-sea rescue aircraft and transport. The ASR models would carry the Lindholme gear (a set of containers of which one contained an inflatable dinghy) or a parachute-dropped Airborne Lifeboat. The latter was 6.1 m long its its Mk.I version and 9.1m in its Mk.II version. The Mk.II lifeboat weighed 1633 kg and could accommodate ten men. The final Warwicks were the GR Mk.II and Mk.V maritime patrol versions, powered by Centaurus engines, which saw limited use at the end of the war.
In 1935 the concept of a twin-engined heavy bomber was considered viable. Indeed the heavy bomber that was then being ordered was the Armstrong Whitworth Whitley, although it would not make its first flight until March of the following year. The first Whitleys had Armstrong Siddeley Tiger radials, although at the outbreak of war these where being replaced by versions with more powerful Rolls-Royce Merlins. By 1942 the Whitley was obsolete as a bomber and its replacement by four-engines heavies was well underway. But it was not pre-ordained that a heavy bomber needed four engines. The determining factor was that the engines of over 2000 hp that designers were hoping for in the late 1930s would arrive with considerable delay, or not at all. Thus it was settled that number of engines became the easy way to distinguish the heavy from the medium bombers, though there were still exceptions.
But this obscured the other potential consideration, the potential difference in operational role. In the autumn of 1940, a strategic bombing campaign appeared the most effective method for Britain to continue the war against Germany. Thus the existing medium bombers were judged by their suitability for long-range bombing, and the Wellington became favoured because it was an effective bomb truck. Usefulness at a tactical and operational level, which was paramount for the Germans, was less of a factor for the RAF. Re-equipping Bomber Command with primarily four-engined heavy bombers made sense, and a growing part of the British industry worked to produce these.
There was still an operational need for smaller bombers, though. Significantly, there was only really successful British venture in this field, though this was an astonishing success: The de Havilland Mosquito. Thanks to a range of modern designs emerging in the US, and Lend-Lease, much of the need for smaller bombers was met by US-built types: The Douglas Boston, Lockheed Ventura, Martin Baltimore, North American Mitchell, and Martin Marauder. British use of these types was important, but because it was not part of the main story of the strategic bombing offensive, it has been largely forgotten.
Flying Guns 