A Medium Bomber for the Ilmavoimat in 1937…….
The plan for the 1937 procurement program made provision for the puchase of a single squadron of medium bombers for the Ilmavoimat (a further squadron was budgeted for in the 1939 program). As with other bomber purchases a strong emphasis was placed on low-altitude tactical bombing rather than “strategic” area bombing from high-altitude. Again and again Somervalo emphasised both to his “bomber” subordinates and to the General Staff that the Ilmavoimat did not have the resources to indulge in the fulfillment of unproven theories and such funding as was available should be concentrated on aircraft which could achieve accurate results, and to date that had only been achieved by low-level bombing strikes and by dive-bombing. As with other purchases over the last half of the 1930’s, the Ilmavoimat conducted a detailed evaluation and testing program – and again, this was for aircraft that were either in production or where prototypes had been completed and were undergoing testing.
As we have seen, in 1935 the Ilmavoimat had purchased 15 Savoia-Marchetti SM.81 bombers and prior to making the decision, had considered the Junkers Ju86, the designs for the Heinkel-111, the Dornier DO 13 and DO 23, the Bloch MB.200, the Potez 540, the Bristol Bombay, the Fairey Hendon, the designs for the Armstrong-Whitworth AW.23, the Handley Page Heyford, the Martin B-10 and the Caproni 122 bomber. In 1937, the Ilmavoimat was looking to purchase a further squadron of some 15-20 medium bombers and a number of the aircraft that had been only in the design stage in 1935 were looked at and evaluated as they were either available as prototypes or were actually beginning to enter production. Medium Bombers evaluated in 1937 included the Armstrong-Whitworth Whitley (UK), Bloch MB.210 (France), CANT Z.1007 (Italy), Fiat BR.20 Medium Bomber (Italy), Handley Page Hampden (UK), Heinkel He111 (Germany), Junkers Ju88 (Germany), Lioré-et-Olivier LeO 45 (France), PZL.37 Łoś (Poland), Savoia-Marchetti SM.79 (Italy) and the Vickers Wellington (UK).
Evaluation criteria heavily emphasized the ability to operate off rough airfields, good speed, manouverability and range, bombload and of course, cost and availability (with an emphasis on certainty of delivery). “Tactical” capability, as opposed to “strategic bombing” was emphasised heavily. The Ilmavoimat under the leadership of Major-General Somervalo had always emphasised support for the Maavoimat – and this was increasingly emphasised through the last half of the 1930s. Two distinct schools of aerial warfare had emerged after WW1 in the writings of air warfare theorists: tactical air warfare and strategic air warfare. Tactical air warfare was developed as part of a combined-arms attack which would be developed to a significant degree by Germany, and which contributed much to the success of the Wehrmacht during the first four years (1939–42) of World War II. The German Luftwaffe became a major element of the German blitzkrieg.
Three of the leading theorists of strategic bombing during this inter-war period were the Italian Giulio Douhet, the Trenchard school in Great Britain, and General Billy Mitchell in the USA. These theorists thought that aerial bombardment of an enemy's homeland would be an important part of future wars. Not only would such attacks weaken the enemy by destroying important military infrastructure, they would also break the morale of the civilian population, forcing their government to capitulate. Although area bombing theorists acknowledged that measures could be taken to defend against bombers – using fighter planes and antiaircraft artillery), the maxim of the times remained "the bomber will always get through". These theorists for strategic bombing argued that it would be necessary to develop a fleet of strategic bombers during peacetime, both to deter any potential enemy, and also in the case of a war, to be able to deliver devastating attacks on the enemy industries and cities while suffering from relatively few friendly casualties before victory was achieved.
Douhet's proposals were hugely influential amongst most airforce enthusiasts, arguing as they did that the bombing air arm was the most important, powerful and invulnerable part of any military. He envisaged future wars as lasting a matter of a few weeks. While each opposing Army and Navy fought an inglorious holding campaign, the respective Air Forces would dismantle their enemies' country, and if one side did not rapidly surrender, both would be so weak after the first few days that the war would effectively cease. Fighter aircraft would be relegated to spotting patrols, but would be essentially powerless to resist the mighty bombers. In support of this theory he argued for targeting of the civilian population as much as any military target, since a nation's morale was as important a resource as its weapons. Paradoxically, he suggested that this would actually reduce total casualties, since "The time would soon come when, to put an end to horror and suffering, the people themselves, driven by the instinct of self-preservation, would rise up and demand an end to the war..." As a result of Douhet's proposals many airforces allocated greater resources to their bomber squadrons than to their fighters, and the 'dashing young pilots' promoted in propaganda of the time were invariably bomber pilots.
Pre-war planners, on the whole, vastly overestimated the damage bombers could do, and underestimated the resilience of civilian populations. The speed and altitude of modern bombers, and the difficulty of hitting a target while under attack from improved ground fire and fighters which had yet to be built was not appreciated. Jingoistic national pride played a major role: for example, at a time when Germany was still disarmed and France was Britain's only European rival, Trenchard boasted, "the French in a bombing duel would probably squeal before we did". At the time, the expectation was any new war would be brief and very savage. A British Cabinet planning document in 1938 predicted that, if war with Germany broke out, 35% of British homes would be hit by bombs in the first three weeks. (This type of expectation should be kept in mind when considering the conduct of the European leaders who appeased Hitler in the late 1930s.). Douhet's theories were successfully put into action in Mesopotamia (modern-day Iraq) where RAF bombers used conventional bombs, gas bombs, and strafed forces identified as engaging in guerrilla uprisings. Arthur Harris, a young RAF squadron commander (later nicknamed "Bomber" Harris), reported after a mission in 1924, "The Arab and Kurd now know what real bombing means, in casualties and damage. They know that within 45 minutes a full-sized village can be practically wiped out and a third of its inhabitants killed or injured."
In Finland, the Ilmavoimat under Major-General Somervalo focused on practicalities, the first of which being that while “strategic” bombing was all very good in theory, the only enemy that Finland faced was the USSR and there was absolutely no possibility that the Ilmavoimat could ever, in its wildest daydreams, build a large enough bomber fleet to conduct an effective strategic bombing campaign against one of the largest and most powerful nations in the world. The second practicality was that ongoing Ilmavoimat trials with the SM.81’s had proven to (almost) everyone’s satisfaction that Douhet’s vision of strategic bombers pounding targets to rubble was incapable of being achieved – accuracy was minimal and from high altitude there was almost no chance of hitting a specific target – in trials, less that 7% of bombs dropped hit within 1,000 feet of their aiming point. In one series of bombing tests from 15,000 feet altitude in good visibility, it took 108 bomber missions dropping 650 bombs in total to achieve 2 hits inside a 400 by 500 ft area. Empiracally, the Ilmavoimat found that very low altitude bombing resulted in very significantly improved accuracy – and that the Curtiss Helldivers and Hawker Harts used as divebombers achieved the highest accuracy (this is something that we’ll explore in a lot more detail when we get to looking at Ilmavoimat doctrine and tactics).
Consequently, in 1937 when looking for a medium bomber, this was where the emphasis was very strongly put. The Ilmavoimat’s bomber force was small – resources could not afford to be wasted and what was wanted was, as has been mentioned above, the ability to operate off rough airfields, good speed, manouverability and range, bombload, cost and availability (with an emphasis on certainty of delivery) and a high level of “Tactical bombing” capability.
The initial shortlist for evaluation consisted of the following aircraft: Armstrong-Whitworth Whitley (UK), Bloch MB.210 (France), CANT Z.1007 (Italy), Fiat BR.20 Medium Bomber (Italy), Handley Page Hampden (UK), Heinkel He111 (Germany), Junkers Ju88 (Germany), Lioré-et-Olivier LeO 45 (France), PZL.37 Łoś (Poland), Savoia-Marchetti SM.79 (Italy) and the Vickers Wellington (UK).
The Douglas B-18 Bolo, North American Aviation XB-21 Dragon and Vickers Wellesley were subsequently added to the evaluation and testing program.
The Armstrong-Whitworth Whitley (UK):
The Armstrong Whitworth A.W.38 Whitley was one of three British twin-engine, front line medium bomber types in service with the Royal Air Force at the outbreak of WW2 (the others were the Vickers Wellington and the Handley Page Hampden). The Whitley was designed by John Lloyd, the Chief Designer of Armstrong Whitworth Aircraft to meet Air Ministry Specification B.3/34 issued in 1934 for a heavy night bomber. The Whitley carried a crew of five and was the first aircraft serving with the RAF to have a (semi ) monocoque fuselage, utilizing a slab-sided structure which eased production. As Lloyd was unfamiliar with the use of flaps on a large heavy monoplane, they were initially omitted. To compensate, the mid-set wings were set at a high angle of incidence (8.5°) to confer good takeoff and landing performance. Although flaps were included late in the design stage, the wing remained unaltered. As a result, the Whitley flew with a pronounced nose-down attitude resulting in considerable drag.
The first prototype Whitley Mk I (K4586) flew on 17 March 1936, piloted by Armstrong Whitworth's Chief Test Pilot Alan Campbell-Orde and was powered by two 795 hp (593 kW) Armstrong Siddeley Tiger IX radial engines. The second prototype was powered by more powerful Tiger XI engines. Owing to the urgent need to replace the old and increasingly obsolete biplane heavy bombers still in service with the RAF, an order for 80 aircraft was placed in 1935, "off the drawing board," before the Whitley had first flown. These had medium-supercharged engines and manual operated drum magazine single machine guns fore and aft. After the first 34 aircraft had been built, the engines were replaced with more reliable two-stage supercharged Tiger VIIIs, resulting in the Whitley Mk II, completing the initial order. The replacement of the manually operated nose turret with a powered Nash & Thomson turret and a powered retractable two-gun ventral "dustbin" turret resulted in the Whitley Mk III. The turret was hydraulically powered but it was hard to operate and added considerable drag.
Early marks of the Whitley had bomb bay doors - the eight bays were in fuselage compartments and wing cells - that were kept closed by bungee cords and opened by the weight of the released bombs falling on them. Even the tiny random delay in time that it took for the doors to open led to highly inaccurate bombing performance. To aim bombs, the bombardier ("Bomb Aimer" in RAF terminology) opened a hatch in the nose of the aircraft which extended the bombsight out of the fuselage. The bombardiers position was in the nose with the front gun turret above. The pilot and second pilot/navigator sat by side by side in the co*ckpit. The navigator rotated so that he could use the chart table behind his seat. Behind the pilots was the wireless operator. The fuselage aft of the wireless operator was divided horizontally by the bomb bay. Aft of the bomb bay was the main entrance and aft of that the rear turret. The Whitley first entered service with No. 10 Squadron in March 1937 replacing Handley Page Heyford biplanes
The Ilmavoimat evaluated the Whitley MkII in early 1937. The Whitley operatred with a Crew of 5 and was powered by 2 × two-stage supercharged Tiger VIII engines with a maximum speed of 230 mph, a range of 1,650 miles and a service ceiling of 26,000 feet. Armament consisted of machinegun in the nose and one in the tail. The Bomb load consisted of up to 7,000 lb (3,175 kg) of bombs in the fuselage and 14 individual cells in the wings, typically including 12 x 250lb bombs and 2 x500lb bombs. Individual bombs as heavy as 2,000lbs could be carried.
The Ilmavoimat evaluation team advised that the Whitley was designed from the start as a “night” bomber, and that it was hardly a modern looking aircraft with its slab-sided fuselage and prominent, jutting chin - and it also had a very distinctive nose-down flying attitude which added considerable drag and reduced performance. It was however, capable of carrying a very impressive bombload of 7,000lb. However, the Armstrong Siddeley Tiger engines were definitely unreliable and the defensive armament was poor. Performance was mediocre and it needed a considerable formed runway to take off. Flying the aircraft and performing tactical bombing missions at low altitude was assessed as being downright dangerous. Overall, the evaluation team rated the Whitley as completely unsuitable for use by the Ilmavoimat in the intended role.
Armstrong Whitworth Whitley cutaway
The Bloch MB.210 (France):
The MB.210 derived from the Bloch MB.200 that the Ilmavoimat had evluated in 1935 and differed from its predecessor by its more deeply-set, cantilever wing and its retractable undercarriage. Developed as a private venture, the prototype MB.210 completed its first flight on 23 November 1934, powered by two 596 kW (800 hp) Gnome-Rhône 14Kdrs/grs air-cooled radial engines. This was followed by a second prototype, the MB.211 Verdun, powered by 641 kW (860 hp) Hispano-Suiza 12Y V-12 liquid-cooled inlines and fitted with a retractable undercarriage, this flying on 29 August 1935. Initial flight testing of this version was somewhat disappointing, so no further examples were built. Further progress with the MB.210, however, convinced the Armée de l'Air to order series production, the first example of which flew on 12 December 1936. The satisfaction did not last very long, however, since it was underpowered and the engines of production aircraft were inclined to overheating. The type was grounded until its engines could be replaced by the more powerful and reliable Gnome-Rhône 14N, these engines first being tested in summer 1937 and had to be replaced. Altogether, 257 units were manufactured amongst companies as diverse as Les Mureaux over Potez-CAMS, Breguet, Hanriot, and Renault.
The Ilmavoimat evaluated the MB.200 as well as the MB.210 and MB.211 prototypes, but considered them no improvement on the MB.200 evaluated in 1935 – indeed, they considred them even more obsolete and ineffective than they were in 1935. The fact that the French were equipping some 12 bomber units with 250 of these already obsolete (in the opinion of the team at least) aircraft caused the Ilmavoimat evaluation team to question whether they should even look at any further French aircraft.
With a crew of 5, maximum speed of 200mph, a range of 1,056 miles, a service ceiling of 32,480 feet and a bombload of 3,520 lbs, the Bloch MB.210 was very much a design inspired by the Douhet doctrine of strategic bombing.
The Ilmavoimat evaluation team also expressed considerable concern about the ability of the French aircraft industry to delivery on any order placed. The French air force had begun a serious rearmament program in 1934 “Plan I”), which called for the production of 1,343 new aircraft. However, in the mid 1930s, the French aircraft industry was more one of scattered and disjointed complexes rather than a cohesive and capable structure. Up to forty organizations had input into nearly all aspects of aircraft design, development and production, while at the same time competing for the designated funding. As it existed in 1937, France’s aircraft industry was not structured to handle large orders and delays ere having a seriously adverse effect on the air force’s rearmament effort. Because of these organizational and structural issues, most of France’s military aircraft of the late 1930s emerged through a narrow technological window. It was a bottleneck which prevented the newly developed aircraft from achieving peak technological capability thus making them obsolete before they even reached operational status.
The problem was compounded by the type of airplanes the French government began to order. Plan I called for the construction of multirole air platforms capable of performing as bombers, fighters and reconnaissance aircraft. Instead of building dedicated platforms, the French government invested in various single type planes. Such aircraft were indeed able to carry out, on a pedestrian basis, each of the various types of missions they were called for, but they could not to distinguish themselves in any single one of them. The decision to develop such platforms was a painful compromise between the Army, the newly formed Air Force and the government. Many inside the air force believed with passion in Giulio Douhet’s strategic theory which called for the destruction of the enemy’s economic strength by destroying its infrastructure while on the other hand, the Army’s senior commanders desired that the new air force serve as a supporting force for the Army rather than as an independent force of its own.
In September 1936, France had developed a new strategic plan, Plan II. Plan II was different from its predecessor in one major area. The new Plan called for the production of up to 1,339 dedicated bombers with a complement of 756 fighters of all types. This shifting in priority towards the bomber had its roots in the new Air Minister Pierre Cot’s passion for Douhet’s strategic vision. Unfortunately for France, Plan II had no more chance of success than its predecessor. Chaos ruled in nearly all French aircraft factories. The problem was accentuated by the Popular Front’s nationalization effort of the mid to late 1930s. As a result of those two factors, France’s aircraft production actually fell during these years. In the spring of 1937, French factories were producing an average of forty units per month. This was five aircraft per month less than in 1936, the year the Germans overtook France in the total number of available airframes. Regardless of the suitability or not of the aircraft, the Ilmavoimat evaluation team expressed strong reservations about the ability of the French aircraft industry to deliver any aircraft ordered with any degree of certainty as to delivery timeframes.
The CANT Z.1007 Alcione (“Kingfisher”) (Italy):
In 1935, Filippo Zappata, the chief designer of the Cantieri Aeronautici e Navali Triestini, designed two medium bombers, the twin-engined CANT Z.1011 and the three-engined CANT Z.1007. Both were to be powered by 619 kW (830 hp) Isotta-Fraschini Asso XI.RC inline engines and were of wooden construction. The Z.1007 design was preferred by both Zappata and the Italian Aviation Ministry, with an order for 18 aircraft being placed on 9 January 1936. A further order for 16 more aircraft followed on 23 February 1937, even before a prototype had been built. It had a crew of five, consisting of two pilots, a flight engineer, a radio operatior and a bombadier/navigator.
The Cant Z.1007 was developed from the Cant Z.506 seaplane, an aircraft that had established many world records in the late 1930s. It was a land-based version and incorporated many improvements, especially on the powerplant. The Z.1007 was a mid-winged monoplane with a retractable tailwheel undercarriage. It had a totally wooden structure, and a very clean shape that was much more aerodynamic than the competing SM.79. The Z.1007 had three engines, with one engine in the nose and two in the wings. The trimotor design was a common feature of Italian aircraft at the time. The aircraft had a slim fuselage as the two pilots sat in tandem rather than side-by-side as in most bombers of the period. Visibility was good and the aircraft was almost a "three-engine fighter" with a very narrow fuselage. This reduced drag, but also worsened the task of the two pilots. The aft pilot had reduced instruments and visibility, and so had difficulty flying and landing the machine if needed; he was almost an 'emergency' pilot. Like most trimotor Italian aircraft of the period the Z.1007 suffered from poor defensive armament, poor engine reliability, and poor power to weight ratio due to low powered engines. The Z.1007 also suffered longitudinal stability problems that were partly rectified later by the adoption of a twin tail arrangement.
The Z.1007 had a defensive armament of four machine guns: two 12.7 mm (.5 in) and two 7.7 mm (.303 in). The main defensive weapon was a Caproni-Lanciani Delta manually-powered Isotta-Fraschini dorsal turret armed with a 12.7 mm (.5 in) Scotti or Breda-SAFAT machine gun. The turret had a good field of fire, although it had blind spot behind the tail. The 12.7 mm (.5 in) Breda was a standard weapon for Italian bombers and the field of fire was improved by the twin-tail configuration on later models. An electrically-powered Breda V turret carrying a similar armament was substituted in late production aircraft. Another 12.7 mm (.5 in) was in the ventral position behind the bomb bay, with a field of fire restricted to the lower rear quadrant of the aircraft. There were also two waist positions equipped with 7.7 mm (.303 in) Breda machine guns, with 500 rpg. Only one of the waist guns could be used at a time since the gunner for this position manned both guns.
The Z.1007 had a horizontal bomb bay which could carry a 1,200 kg (2,650 lb) bombload. Many other Italian aircraft had vertical bomb bays which not only limited accuracy, but also limited the size of bombs carried internally. There were also a pair of under-wing hard points which could carry up to 1,000 kg (2,200 lb) of bombs, giving the Z.1007 a potential 2,200 kg (4,900 lb) payload (to a maximum range of 640 km/400 mi), but the norm was 1,200 kg and 1,000 km range. The Z.1007's external hardpoints were a rarity in the bombers of the Regia Aereonautica. The Z.1007 could also carry two 454 mm (17.7 in), 800 kg (1,760 lb) torpedoes slung externally under the belly in an anti-shipping role, an option which was never used in Italian service. The bombardier's nacelle was near the wings, just below the pilot. This improved the layout compared to the SM.79, where the nacelle was almost in the tail section, with the double task of being a defence position with a machine gun mounted there.
The first prototype flew in March 1937, proving superior to the Z.1011, with its handling and manoeuvrability being praised. Its performance, however, was lower than predicted, and Zappata therefore started a major redesign of the Z.1007, production of the initial version being limited to the existing orders placed before the prototype flew. However, this was the aircraft that the Ilmavoimat evaluated. Major concerns were the poor power to weight ratio due to the low powered engines. The test pilots also expressed concerns about the longitudinal stability problems that had resulted in Zapatta beginning a redesign. These concerns were sufficient to ensure that the Ilmavoimat dropped the aircraft from further consideration.
OTL Note: After much experimentation with the prototype, the production aircraft were fitted with annular radiators so their profile was similar to radial engines that would be fitted to the improved later versions. It had "excellent flying characteristics and good stability.” Delivery of production Asso powered Z.1007s started in February 1939, with production ending in October that year. The first Asso-powered Z.1007s were used to equip the 50° Gruppo of the 16° Stormo (i.e. the 50° Gruppo of the 16° Stormo) from May 1939. The Asso powered bombers were not considered suitable for operational use, however, owing to the unreliability of their and high maintenance requirements, while their defensive armament was considered inadequate. They were therefore used as trainers. Zappata had, meanwhile, continued the development of a considerably changed version, the Z.1007bis , to resolve the problems with the original aircraft. While the new version was of similar layout, it was effectively a completely new design. Three Piaggio P.XI RC.40 radial engines, a derivative of the French Gnome-Rhône 14K) of 736 kW (986 hp) takeoff power replaced the less powerful and unreliable liquid cooled engines of the original version. The bis was longer with wings of greater span and area, while the aircraft was considerably heavier, weighing 580 kg (1,280 lb) more unladen, with a maximum takeoff weight 888 kg (1,960 lb) greater, while it carried heavier offensive and defensive armament. The prototype bis first flew in July 1939, with testing proving successful, with the Z.1007bis being ordered into large scale production, with deliveries of pre-production aircraft starting late that year.
Cant Z.1007 “Alcione”s over Greece.
When Italy entered World War II on 10 June 1940, the Regia Aeronautica had two Stormi equipped with the "Alcione". One was the 16°, with 31 aircraft, equipped with the Isotta Fraschini engine and so declared "non bellici", "not suitable for war." The 47° Stormo had just received four CANT bis. The "Alcione" had its baptism of fire on 29 August 1940 when they began to be used for attacks on Malta, they were later involved in the attack on Greece, and then in the later stages of the Battle of Britain and after that, against Yugoslavia. Later in WW2 the Z.1007s were used mainly as night bombers and reconnaissance, they were also used for long range reconnaissance, with excellent results. Some, at least 20, were equipped with an auxiliary tank that gave 1,000 km (620 mi) extra endurance. Some were adapted for flare drops when day missions were too dangerous.
The Caproni Ca.135 (Italy)
General Valle (Chief of Staff of the Regia Aeronautica) initiated the "R-plan" - a program designed to modernize Italy's air force, and to give it a strength of 3,000 aircraft by 1940. In late 1934 a competition was held for a bomber with the following specifications: A speed of 210 mph) at 14,800 ft and 239 mph at 16,000 ft), a range: of 620 miles with a 2,600 lb bombload and a ceiling of 26,000 feet. The ceiling and range specifications were not met, but the speed was exceeded by almost all the machines entered. At the end of the competition, the "winners" were the Ca.135 (with 204 aircraft ordered), the Fiat BR.20 (204 aircraft ordered), the Piaggio P.32 (144 aircraft ordered), the Savoia-Marchetti SM.79 (96 ordered), the CANT Z.1007 (49 ordered), and the Piaggio P.32 (12 ordered). This array of aircraft was proof of the anarchy, clientelarism, and inefficiency that afflicted the Italian aviation industry. Worse was the continuous waste of resources by the Regia Aeronautica (Italian Royal Air Force). Orders were given for aircraft that were already obsolete. The winners of the competition were not always the best - the BR.20 was overlooked in favour of the SM.79, an aircraft which was not even entered in the competition.
The Caproni Ca.135 was an Italian medium bomber designed by Cesare Pallavicino of CAB (Caproni Aereonautica Bergamasca). The Ca.135 was to be built at Caproni's main Taliedo factory in Milan. However, the project was retained at Ponte San Pietro and the prototype, completed over 1934-35, (a long construction time for the period), was first flown on 1 April 1935. The new bomber resembled the Caproni Ca.310, with its rounded nose, two engines, low-slung fuselage and wings with a very long chord. Several versions were fitted with different engines and some had noticeable performance differences. The prototype was powered by two 623 kW (835 hp) (at 4,000 m/13,123 ft) Isotta-Fraschini Asso XI.RC radial engines initially fitted with two bladed wooden propellers. Structurally, it was built of mixed materials, with a stressed-skin forward fuselage and a wood and fabric-covered steel-tube rear section; the wings being of metal and wood, using fabric and wood as a covering. The wings were more than ⅓ of the total length, and had two spars of wooden construction, covered with plywood and metal. The tail surfaces were built of wood covered with metal and plywood. The fuel system, with two tanks in the inner wings, held a total of 2,200 L (581 US gal).
Caproni Ca 135 Prototype
The Ca.135's fuselage shape was quite different from, for example, that of the Fiat BR.20. If the latter resembled the American B-25 Mitchell, the Ca.135, with its low fuselage more resembled the American B-26 Marauder. Its long nose accommodated the bomb-aimer (bombardier) and a front turret (similar to the Piaggio P.108 and later British bombers). The front part of the nose was detachable to allow a quick exit from the aircraft. It also had two doors in the co*ckpit roof, giving the pilots the chance to escape in an emergency. The right-hand seat could fold up to assist entry to the nose. A single 12.7 mm (0.5 in) machinegun in a turret in mid-fuselage, was manned by the co-pilot. A seat for the flight engineer was later fitted. The wireless operator's station, in the aft fuselage, was fitted with the AR350/AR5 (the standard for Italian bombers), a radiogoniometer (P63N), an OMI AGR.90 photographic-planimetric machine or the similar AGR 61. The aircraft was also equipped with an APR 3 camera which although not fixed, was normally operated through a small window. The wireless operator also had a 12.7 mm (0.5 in) machine gun in the ventral position. All this equipment made him very busy; as a result, an extra man was often carried. The aircraft had very wide glazed surfaces in the nose, co*ckpit, and the central and aft fuselage; much more than in other Italian aircraft.
Overall, the aircraft was fitted with three machine guns, of 12.7 mm (0.5 in) calibre in the turrets, and a 7.7 mm (0.303 in) calibre gun in the nose. All had 500 rounds, except the 7.7 mm (0.303 in) which had 350. Bombload, like most Italian bombers, was less than impressive in terms of total weight, but was relatively flexible, depending on the role - from anti-ship to close air support and a maximum 4,105lb bombload could be carried – or alternatively 2 × torpedoes (never used, but hardpoints were fitted). The aircraft was underpowered, with a maximum speed of 226 mph at 14,800 ft and a high minimum speed of 81 mph (there were no slats, and maybe not even flaps). The Service Ceiling was only 20,000 ft and the endurance, at 70% of throttle, was 990 miles. All-up weight was too high, with total of 819,240 lb, not the 16,260 lb expected.
The total payload was shared between the crew, weapons, radios and other equipment, fuel, oil, oxygen and bombs. There was almost no chance of carrying a full load of fuel with the maximum bombload. The lack of power made take-offs when over-loaded, impossible. Indeed, even with a normal load, take-offs were problematic. Take-off and landing distances were 418 m (1,371 ft) and 430 m (1,410 ft). The range was good enough to assure 2,200 km (1,400 mi) with 550 kg (1,210 lb) and 1,200 km (750 mi) with 1,200 kg (2,650 lb). The ear;y production version was fitted with two inline liquid-cooled Asso XI RC.40 engines, each giving 671 kW (900 hp) at 4,000 m (13,120 ft). Aerodynamic drag was reduced, with three-bladed metal propellers that were theoretically more efficient. These new engines gave the aircraft a maximum speed of 400 km/h (250 mph) at 4,000 m (13,120 ft). It could climb to 2,000 m (6,560 ft) in 5.5 minutes, 4,000 m (13,120 ft) in 12.1 minutes and 5,000 m (16,400 ft) in 16.9 minutes.
Despite this, the aircraft was still underpowered. The aircraft evaluated by the Ilmavoimat yawed to the right on take-off, had poor lateral stability; the engines (from comments made by the Italian pilots) were unreliable in service, and the bombers suffered a excessive number of oil and hydraulic leaks during testing. The Ca 135 was also assessed as being dangerously underpowered and lacking in defensive armament. As a result, the test team made strong recommendations against this aircraft.
Caproni Ca 135
The Douglas B-18 Bolo (USA):
In 1934, the United States Army Air Corps put out a request for a bomber with double the bomb load and range of the Martin B-10, which was just entering service as the Army's standard bomber. In the evaluation at Wright Field the following year, Douglas showed its DB-1. It competed with the Boeing Model 299 (later the B-17 Flying Fortress) and Martin Model 146. While the Boeing design was clearly superior, the crash of the B-17 prototype (caused by taking off with the controls locked) removed it from consideration. During the depths of the Great Depression, the lower price of the DB-1 ($58,500 vs. $99,620 for the Model 299) also counted in its favor. The Douglas design was ordered into immediate production in January 1936 as the B-18. The initial contract called for 133 B-18s (including DB-1), using Wright R-1820 radial engines. The last B-18 of the run, designated DB-2 by the company, had a power-operated nose turret. This design did not become standard. An additional contract was placed in 1937 for a further 177 aircraft.
The DB-1 design was essentially that of the DC-2, with several modifications. The wingspan was 4.5 ft (1.4 m) greater. The fuselage was deeper, to better accommodate bombs and the six-member crew; the wings were fixed in the middle of the cross-section rather than to the bottom, but this was due to the deeper fuselage. Added armament included nose, dorsal, and ventral gun turrets. Production B-18s, with full military equipment fitted, had a maximum speed of 217 mph, cruising speed of 167 mph, and combat range of 850 miles. The Bolo carried a 4,400lb bombload and was armed with 3 × .30 in (7.62 mm) machine guns.
The Ilmavoimat evaluation team considered the Bolo soundly designed and built but underpowered, carrying too small a bomb load and with limited defensive armament. The aircraft remained in consideration however.
One thing that was evident to the Ilmavoimat Team was that Douglas would certainly be able to fulfill any orders placed. The manufacturing facilities were impressive!
The Fiat BR.20 Medium Bomber (Italy):
In 1934, Regia Aeronautica requested Italian aviation manufacturers to submit proposals for a new medium bomber; the specifications called for speeds of 330 km/h (205 mph) at 4,500 m (15,000 ft) and 385 km/h (239 mph) at 5,000 m (16,400 ft), a 1,000 km (620 mi) range and 1,200 kg (2,600 lb) bombload. Although Piaggio, Macchi, Breda, Caproni and Fiat offered aircraft that mainly exceeded the speed requirements (but not range), not all exhibited satisfactory flight characteristics or reliability. Accepted among the successful proposals, together with the trimotor Savoia-Marchetti SM.79 and Cant Z.1007, was the Fiat BR.20 Cicogna designed by Celestino Rosatelli, thus gaining the prefix BR, (for "Bombardiere Rosatelli"). The BR.20 was designed and developed quickly, with the design being finalised in 1935 and the first prototype (serial number M.M.274) flown at Turin on 10 February 1936. Production orders were quickly placed, initial deliveries being made to the Regia Aeronautica in September 1936. When it entered service in 1936 it was the first all-metal Italian bomber and it was regarded as one of the most modern medium bombers available anywhere.
The BR.20 was a twin-engine low-wing monoplane, with a twin tail and a nose separated into co*ckpit and navigator stations. Its robust main structure was of mixed-construction; with a slab-sided fuselage of welded steel tube structure having duralumin skinning of the forward and centre fuselage, and fabric covering the rear fuselage. The 74 m² (796 ft²) metal-skinned wings had two spars and 50 ribs (also made of duralumin), with fabric-covered control surfaces. The hydraulically actuated main undercarriage elements retracted into the engine's nacelles, and carried 106 x 375 x 406 mm wheels. The takeoff and landing distances were quite short due to the low wing loading, while the thickness of the wing did not compromise the aircraft's speed. The twin tail allowed a good field of fire from the dorsal gun turret.
The engines were two Fiat A.80 RC 41s, rated at 1,000 cv at 4,100 m (13,451 ft), driving three-blade Fiat-Hamilton metal variable-pitch propellers. Six self-sealing fuel tanks in the centre fuselage and inner wings held 3,622 Ls of fuel, with two oil tanks holding 112 L. This gave the fully-loaded bomber, (carrying a 7,900 lb payload) an endurance of 5½ hours at 350 km/h (220 mph), and 16,400 ft altitude. Takeoff and landing distances were 350 m (1,150 ft) and 380 m (1,250 ft) respectively. The theoretical ceiling was 24,930 ft. Crewed by four or five, the BR.20's two pilots sat side-by-side with the engineer/radio operator/gunner behind. The radio operator's equipment included an R.A. 350-I radio-transmitter, A.R.5 receiver and P.3N radio compass. The navigator/bomb-aimer had a station in the nose equipped with bombsights and a vertical camera. Another two or three crewmembers occupied the nose and the mid-fuselage, as radio-operator, navigator and gunners. The radio operator was also the ventral gunner while the last crew member was the dorsal gunner.
The aircraft was fitted with a Breda model H nose turret carrying a single 7.7 mm (.303 in) Breda-SAFAT machine gun, and was initially fitted with a Breda DR dorsal turret carrying one or two 7.7 mm (.303 in) machine guns. This turret was unusual because it was semi-retractable: the gunner's view was from a small cupola, and in case of danger, he could extend the turret. The aircraft was fitted with a further 7.7 mm (.303 in) machine gun in a ventral clamshell hatch that could be opened when required. The BR.20's payload was carried entirely in the bomb bay in any of the following possible combinations: 2 × 800 kg (1,760 lb) bombs as maximum load, 2 × 500 kg (1,100 lb), 4 × 250 kg (550 lb), 4 × 160 kg (350 lb), 12 × 100 kg (220 lb), 12 × 50 kg (110 lb), 12 × 20 kg (40 lb), or 12 × 15 kg (30 lb) bombs. Combinations of different types were also possible, including 1 × 800 kg (1,760 lb) and 6 × 100 kg (220 lb), 1 × 800 kg (1,760 lb) and 6 × 15 or 20 kg (30 or 40 lb), or 2 × 250 kg (550 lb) and 6 × 50 or 100 kg (110 or 220 lb) bombs. The BR.20 could also carry four dispensers, armed with up to 720 × 1 or 2 kg (2 or 4 lb) HE or incendiary bomblets. All the bombs were loaded and released horizontally, improving the accuracy of the launch.
With a Crew of 5, the BR.20 was powered by 2 × Fiat A.80 RC.41 18-cylinder radial engines of 746 kW (1,000 hp) each giving a maximum speed of 273mph, a range of 1,709 miles and a service ceiling of 26,250 feet. Defensive armament consisted of 3× 12.7 mm (.5 in) Breda-SAFAT machine guns in nose, dorsal and ventral positions. A 3,530lb bombload could be carried.
The Ilmavoimat evaluation team considered the BR.20 a remarkably good aircraft that could be improved somewhat by increased engine power and heavier armament. They reommended that consideration be given to a gunship ground attack version fitted with nose-mounted cannon, a tricycle undercarriage and armour protection for the crew – and as with the Polish PZL 37, they considered that for Ilmavoimat use, 2 crew positions could be eliminated - the ventral gunner and the bombardier / nose gunner.
The Handley Page Hampden (UK):
The Handley Page HP.52 Hampden was a British twin-engine medium bomber designed or the RAF to the same specification as the Wellington (Air Ministry Specification B.9/32). The first production batch of 180 Mk I Hampdens was built to Specification 30/36. Conceived as a fast, manoeuvrable, "fighting bomber", the Hampden had a fixed .303 in (7.7 mm) Vickers K machine gun in the forward fuselage. To avoid the weight penalties of powered-turrets, the Hampden had a curved Perspex nose fitted with a manual .303 in (7.7 mm) Vickers K gun and two more single .303 in (7.7 mm) Vickers K installations in the rear upper and lower positions. The layout was similar to the all-guns-forward co*ckpits introduced about the same time in the Luftwaffe's medium bombers, notably the Dornier Do 17.
Construction was from sections prefabricated then joined. The fuselage was in three major sections - front, centre and rear. The centre and rear sections were themselves made of two halves. This meant the sections could be fitted out in part in better working conditions before assembly. In a similar way, the wings were made up of three large units - centre section, port outer wing and starboard outer wing - which were in turn sub-divided. The Hampden was a stressed skin design reinforced with a mixture of bent and extruded sections. The wing used a single main spar. The first prototype flew on 21 June 1936. Crewspace was cramped and there were a number of blindspots in the defense. Due to the short and narrow fuselage and long tail boom it was soon nicknamed “Flying Suitcase.”
With a Crew of 4 (Pilot, navigator/bomb aimer, radio operator and rear gunner), the Hampden was powered by 2 × Bristol Pegasus XVIII 9-cylinder radial engines of 980 hp (730 kW) each giving a maximum speed of 265mph, a ramge of 1,095 miles and a service ceiling of 19,000 feet. Defensive armament consisted of 4-6 × .303 in (7.7 mm) Vickers K machine guns: one flexible and one fixed in the nose, one or two each in the dorsal and ventral positions. A maximum 4,000lb bombload or 1 Torpedo could be carried.
OTL Note: A total of 1,430 Hampdens were built: 500 by Handley Page, 770 by English Electric at Samlesbury in Lancashire; and in 1940–41, 160 in Canada by the Canadian Associated Aircraft consortium (although some were retained in Canada, 84 were shipped by sea to the United Kingdom). The Hampden wasn't good at daylight bombing as it had many blind spots for defense and the crew was very cramped in the narrow confines (3 feet wide at the widest point) of the fuselage. It proved to have a totally inadequate defensive armament. Heavy losses were suffered on day bomber missions. The Hampden was abandoned by RAF Bomber Command in 1942. Some were then converted to torpedo bombers.
The Heinkel He111 (Germany):
Tthe Heinkel He 111 had been designed earlier in the 1930s by Siegfried and Walter Günter. The first He 111 flew on 24 February 1935 and while the Ilmavoimat had rejected the civilian passenger aircraft as too small for the military transport they were then looking for, they were interested in the bomber version. In May 1935 evaluation flights of both the Junkers Ju86 and Heinkel He111 had been flown. Performance of the He111 was good – a speed of 255mph, a range of 1429 miles with maximum fuel and a bomb load of 2000kg internally (8 x 250kg bombs). However, the aircraft was still in development, delivery times could not be guaranteed and the cost as compared to the Italian SM.81 aircraft that in the end was selected as a bomber (in 1935) was on the high side. However the Ilmavoimat remained interested and in 1937 they re-evaluated the aircraft.
In 1935, when the Ilmavoimat had first evaluated the aircraft, the Heinkel was equipped with two BMW VI engines and the maximum speed was 311 km/h (193 mph). By early 1937, a number of prototypes with 9ncreasingly more powerful engines and better wing designs had been built – the Ilmavoimat at this stage tested a military bomber variant – the He111B-1. The bomb load was now 1,500 kg (3,300 lb), while there was also an increase in maximum speed and altitude to 215 mph (344 km/h) and 22,000 ft and the armament settled at three machine gun positions. Construction had begun at the Heinkel factory at Oranienburg and Heinkel assured the Finns that any order they placed could be met (mentioning also that the Turkish Air Force were negotiating to buy a number of the aircraft). The evaluation team rated the He111 highly.
With a Crew of 4 (pilot, navigator/bombardier/nose gunner, ventral gunner, dorsal gunner/radio operator), the He111 had a maximum speed of 215mph, could carry a 3,300lb bombload with a range of 1,429 miles and had a service ceiling of 22,000 feet.
Heinkel He111 of the Condor Legion in Spain. Ilmavoimat volunteers went on to fly the aircraft operationally in Spain and praised its performance highly. However, despite the 1935 amd 1937 evaluations which gave the aicraft high marks, it was never purchased by the Ilmavoimat
The Junkers Ju88 (Germany):
In August 1935, the Reichsluftfahrtministerium submitted its requirements for an unarmed, three-seat, high-speed bomber, with a payload of 800-1,000 kg (1,760-2,200 lb). Junkers presented their initial design in June 1936, and were given clearance to build two prototypes (Werknummer 4941 and 4942). The first two aircraft were to have a range of 2,000 km (1,240 mi) and were to be powered by two DB 600s. Three further aircraft, (Werknummer 4943, 4944 and 4945), were to be powered by Jumo 211 engines. The first two prototypes, Ju 88 V1 and V2, were different from the V3, V4 and V5 in that the latter three models were equipped with three defensive armament positions to the rear of the co*ckpit, and were able to carry two 1,000 kg (2,200 lb) bombs under the inner wing.
The first five prototypes had conventionally-operating dual-strut leg rearwards-retracting main gear, but starting with the V6 prototype, a main gear design that twisted the new, single-leg main gear strut through 90° during the retraction sequence debuted, much like the American Curtiss P-40 fighter design used. This feature allowed the main wheels to end up above the lower end of the strut when fully retracted [N 1] and was adopted as standard for all future production Ju 88s, and only minimally modified for the later Ju 188 and 388 developments of it. These single-leg landing gear struts also made use of stacks of conical Belleville washers inside them, as their main form of suspension for takeoffs and landings.
The aircraft's first flight was made by the prototype Ju 88 V1, which bore the civil registration D-AQEN, on 21 December 1936. When it first flew, it managed about 580 km/h (360 mph) and Hermann Göring, head of the Luftwaffe was ecstatic. It was an aircraft that could finally fulfill the promise of the Schnellbomber, a high-speed bomber. The streamlined fuselage was modeled after its contemporary, the Dornier Do 17, but with fewer defensive guns because the belief still held that a high speed bomber could outrun late 1930s-era fighters. However, production was delayed drastically with developmental problems and this was the situation when the Ilmavoimat assessed the prototype in early 1937.
Junkers Ju88 V1 Prototype evaluated in early 1937
At this stage, the Ilmavoimat team liked the aircraft and could see its potential with its projected bombload of 6,600lb and a speed of 300mph+. However, with the problems still being worked on, a number of prototypes in development and production not yet in sight, the team recommended a “wait and see” approach with a further evaluation to be carried out in 1938.
...to be continued in the next post
