The sheer numbers of aircraft required by World War II demanded novel methods of acquiring tactical superiority with extreme haste. Given the massive production numbers of existing types, it frequently made sense to redesign the existing airframes, and avoid spending a crucial time developing from scratch. The consequence was often truly unusual designs, including attack bomber escorts armed to the teeth, floatplane fighters, aerial mine-sweepers, high altitude interceptors, and even carrier planes that flew in the hold!

These modifications were designed around the particular problems of war. Most performed too poorly, or too well and required such immense risk that none of their lessons were learned but this gave rise to some wonderful aircraft whose designs were to carry across to future generations, however not to the extent that it should be, and from YB-40s & B-25s gunships from USA and Mistel Composites & Zveno systems from Germany& USSR, some magnificent but also some incredibly peculiar machines were born due to limitations being stretched to the limit.

1. US Heavy Bomber Fighter Conversions: YB-40 and XB-41

From a tactical point of view at the start of the war the ability to transform fighters into light bombers took place very often, whereas the opposite transformation had much less of an occurrence. It was also asked of the United States Army Air Forces whether to modify heavy bombers into escorted gunships that would provide escort of bomber streams over Europe. The topic had been topical as long as the possibility of having single fighter aircraft at the disposition of a bomber stream that would fly with it all the way from Britain to Germany and back did not really exist. It turned out that the first attempt (XB-41 which was a converted B-24 Liberator but mounted with fourteen .50-caliber machine guns and over 14,000 rounds of bullets) had testing problems so they looked into Boeing’s conversion for the B-17 Flying Fortress (designated as YB-40).

YB-40’s Firepower Story:

• Built from B-17 bombers
• Up to thirty defensive guns
• Twenty-five aircraft were built
• Tested on ten missions
• Excess weight reduced speed

An interesting concept that attempted to turn a bomber into more of an “aerial gun platform” or “floating defensive fortress,” the YB-40 was intended not as a bomb delivery platform, but a supplementary defensive platform for bomber formations that were somewhat exposed on long range missions. Its design showed the pressing need for defines before such aircraft as the P-51 Mustang, long-range fighters, became available. Although the prototype XB-40 showed just how far the idea could be taken to extremes, a 14 x .50 inch machine-gun armed B-24 conversion failed to win enough favor to carry through into full production. The YB-40 presented a better configuration and possessed a formidable compliment of defensive weapons but was hampered in other ways, which led to central issue of the equipment causing all the difficulties.

2. Grumman XF4F-3S ‘Wildcatfish’

A couple of land-based fighters were adapted into floatplanes during the course of the war-these were intended to be launched from out of the way places that lack conventional airfields. In part because of the way Japan was employing floatplane fighters from remote bases in the Pacific, in 1942 Edo was awarded a contract to design and develop a water-compatible modification of the basic Grumman F4F-3 Wildcat carrier-based fighter. The premise of such adaptation should be fairly easy to picture: take a standard, carrier-capable plane and modify it so it can launch and land on water as well as prepared airfields. Two large floats on struts, ventral fin and more tail fins to balance the airframe were needed to make the conversion feasible. The Wildcat was already much slower than the Japanese Mitsubishi Zero; drag introduced by the flotation gear knocked speed off another 5mph, meaning the aircraft could be operated only where friendly fighters had removed the opposition.

Wildcatfish Conversion Highlights:

• Based on the F4F-3 Wildcat
• Fitted with two large floats
• Top speed fell considerably
• One prototype was built
• Island bases ended its need

Here again is another case of the seemingly realistic conversion proving redundant due to rapid developments on the battlefield exceeding production runs. Already serving as an adequate and invaluable carrier-based fighter and being a handy aircraft for operating within the conditions encountered in the Pacific, fitting large floats only presented added drag and decreased its airspeed exactly when more and more desirable. The concept then had to be designed for circumstances in which it was the case that enemy aircraft were not a real factor. While plans for 100 sets of floats indicated the planners originally may have had high expectations, only one full airframe was ever completed.

3. Aerial Minesweepers

During the initial phase of the war, naval magnetic mines came to pose a grave threat to shipping and by the end of 1939, 79 ships had been lost to them. The British took a curious aircraft-mounted solution to the problem, modifying Wellington bombers into aerial minesweepers. Instead of using ships in order to locate and remove the mines, they fitted the Wellington bombers with very large 48-foot diameter rings fashioned from balsa wood, complete with electrical coils in order to mimic a ship with magnetic induction pulses. The bombers flew at 130 mph at just 35 to 60 feet over the water. Thus, with the magnetic gear enabled on the bottom of the Wellingtons they were able to detonate the moored mines on top. It was an immensely dangerous job as this involved flying at an extremely low altitude and knowingly provoking massive Underwater explosions, but the reconditioned Wellingtons were instrumental in keeping the Thames Estuary clear throughout the duration of the war.

Aerial Minesweeping Essentials:

• Wellington bombers became sweepers
• Massive 48-foot magnetic ring
• Flew extremely close to water
• Magnetic impulses triggered mines
• Cleared the Thames Estuary

What made this airborne minesweeper peculiar was that the airplane itself was also part of the trigger mechanism: A huge ring of balsa wood and several electrical coils, set up in an attempt to recreate the magnetic field of a ship that ordinarily travelled through the water. Flying over a mine field, it would trigger mines automatically as it was the cheapest option compared to letting a traditional minesweeper Plow into the field. Still the crews’ role was a hazardous one; only 35 to 60 feet above the sea gives a very small area of error, and even greater risk attended the air-delivered operation.

4. High-Altitude Combat: Ju 86 and Spitfire

By 1939 Junkers adapted its ageing Ju 86 medium bomber into a highly specialized high altitude reconnaissance aircraft called the Ju 86P. Pressurised cabins, turbocharged diesel engines and a longer wing span were fitted, allowing these aircraft to cruise at approximately 40,000 feet without ill effect on the crew. Forty of these Ju 86P aircraft were used against Britain for reconnaissance and harassing bomb attacks in their incredibly high operating ceiling, at first these ‘wonder-bombers’ eluded British interception, proving how a bombers original design can have a radical new tactical profile attributed by operating at altitude. Junkers had developed the Ju 86R with more massive wings; it could operate around 47,000ft. Britain eventually produced pressurised versions of the Spitfire Mks VI and VII while lighter Spitfire IX airframes were modified to fly at very great altitude, and a slightly lightened Spitfire IX flew from Egypt against a Ju 86 that it hit in August 1942 at a height of 44,000ft.

High-Altitude Combat Facts:

• Ju 86P reached 40,000 feet
• Pressurised cabin aided altitude
• Ju 86R reached 47,000 feet
• Spitfires were modified too
• Combat occurred at 44,000 feet

Altitude became protection as shown on the Ju 86P conversion. Rather than rely on speed, manoeuvrability and a heavy defensive armament, the conversion’s strategy was that the aircraft would fly in places that no conventional fighter could go to. A pressurised cabin and turbodiesel engines enabled altitude to be sustained over a long period, and the extended wings gave the lift to do so. This was however, a temporary lull and British designers developed specific high-altitude Spitfires and the German threat in the air over high altitudes diminish accordingly, though one occasion in August 1942 in Egypt in a Dog Fight, showed that the altitude gap could be eliminated.

5. Fieseler Fi 103R ‘Reichenberg’

This is one of the most extreme variations made of any aircraft during the war: the Fieseler Fi 103R ‘Reichenberg’ was a V-1 flying bomb with an even smaller cockpit added behind its 900kg warhead. The reason that a pilot was to man the aircraft was that the standard unguided and notoriously inaccurate V-1 was not able to engage ships or tactical targets in an effective manner. While the aircraft was never designed to be simply a suicide weapon at least that does not mean the pilot had more than a 1% chance of survival in an attack. The presence of the pulsejet intake behind the cockpit canopy made the possibility of a dangerous escape from the aircraft a critical issue. Candidates were trained on gliders, including converted examples that had been fitted for extremely high-speed diving, and still had more training to do on a twin-seat, powered variant of this aircraft called the R-III.

Reichenberg’s Extreme Design:

• Based on the V-1 flying bomb
• Carried 900kg warhead
• Added a cramped cockpit
• Survival chances were minimal
• Never entered combat

This would, as you could see, represent where Germany was very short late in the war. Basically, the Reichenberg was supposed to be a plane designed to crash from pilot guidance into valuable things like ships and such. Ideally the pilot would bail out seconds before crash but this plane did not really design a safe bail out system. The training for the program had to use gliders as the pilot had to learn the novel handling characteristics of the plane and to understand its very high-speed capabilities. The first flight of the Fi 103R took place in September 1944 and ended on the ground while a second crashed a day later during a flight, revealing to the world the flaws of the notion.

6. Rotabuggy and Antonov A-40

Experimentation did not just extend to the design of an aircraft within wartime flying technology. Some attempts to even convert normal land vehicles to that flying and could then transported by air and supplied to various locations as need dictated. Austrian engineer Raoul Hafner designed the Rotabuggy by mounting an unpowered rotor on to a jeep built in Great Britain. It was intended that the Rotabuggy would be towed by aircraft and then released, where the rotor would create the lift so it was allowed to fly, or more specifically glide to where it was being needed to be delivered. In September 1944 tests were held when the Rotabuggy was launched from a Whitley tug. The flying Jeep flew for just under ten minutes before landing at 65 mph and was reported to have good flight characteristics but gliders that carried Jeeps meant it was not required; the Soviets pushed the concept even further when they took a T60 light tank and converted it into a glider. Designer Oleg Antonov fixed disposable bi-plane wings and tail to the vehicle, enabling it to actually fly during tests in September 1942.

Flying Vehicle Experiments:

• Rotabuggy used an unpowered rotor
• Tested behind a Whitley
• Flew for ten minutes
• T-60 became a tank glider
• Powerful tug aircraft was lacking

The Rotabuggy epitomises just how far the British armed forces might consider the designs of their military vehicles to go if conventional modes of transportation were unavailable. The car effectively became a rotorcraft without an engine. The ten-minute flight test was enough to make engineers understand it was possible to design and successfully test. It didn’t automatically mean the vehicle would be useful for what it was intended. The Soviet T-60 project took this further by strapping wings and tail to a light tank. It managed to fly, then was driven home after testing; however, this simply showed the tank could fly and not, more crucially whether a tug Aircraft could fly it appropriately.

7. B-25 Gunships

A combination of modifications during the war, converted the B-25 medium bomber, into a very powerfully gun-armed attack aircraft; perhaps the hardest-hittest attack plane of the war. The B-25 came into Major ‘Pappy’ Gunn’s control, while he was stationed in Australia and during that time developed the B-25 into this heavily gun-armed attack plane by mount a further eight .50-calibre machines guns to fire forward and also installed into four more machines guns into the nose in the forward cockpit: these machines became known as “Commerce Destroyers,” and were utilized to attack shipping from Japanese control and eleven, of these “Commerce Destroyers,” performed a crucial role in the Battle of the Bismarck Sea, in cooperation with skip-bombing attacks. These field modifications proved so successful that dedicated factory-built B-25G and B-25H variants were constructed. This “H” variant was particularly lethal and carried the large 75mm cannon obtained by re-rifling a Sherman tank main gun along with ten forward firing .50 cal machineguns.

B-25 Gunship Firepower:

• Eight guns in early conversions
• Known as Commerce Destroyers
• Used against Japanese shipping
• B-25H carried 75mm cannon
• Ten forward .50-calibre guns

In a sense, the B-25 gunship conversion was an embodiment of battlefield improvisation during wartime. Major ‘Pappy’ Gunn and his crew did not wait for a completely redesigned aircraft to enter production; instead, they re-configured a existing bomber to launch a high concentration of forward firing armaments at Japanese vessels. The gunship combined with skip bombing resulted in an aircraft that was effective during ship attack missions. This enhanced weapon configuration not only improved the aircraft, but it translated directly into factory production.

8. Mistel Composite Aircraft

The Mistel system (meaning ‘mistletoe’ in German) was an unholy union between two aircraft that had been produced individually and merged to become a “composite strike aircraft”. In its standard layout it consisted of the piloted fighter aircraft, often a Bf 109 or Fw190, above an unmanned Ju88 bomber whose cargo was a two-tonne shaped charge explosive. During the approach to the target-the bomber, carrying the explosive, would be controlled by the fighter pilot which he would fly into the target and then he would detach his fighter and fly it back to the base. The concept eventually became operational service during 1944 following promising initial test unit developments within Luftwaffe test unit KG 200 codenamed ‘Beethoven.’

Mistel Composite Features:

• Fighter mounted above bomber
• Ju 88 carried explosives
• Pilot guided combined aircraft
• Fighter detached before impact
• Accuracy remained a problem

The Mastel concept, which utilized old bombers to exploit their remaining potential and act as “remotely operated guided bombs”, ensured that a bomber was not used with its full complement of bomb-aimers and crew aimed at their final target, instead the entire crew section was removed from the bomber which was packed with a substantial shaped charge and directed towards its target via controls on the fighter carried on top of it. Following the release of the bomb, the system theoretically provided the pilot with an escape plan, though this depended critically upon being able to launch its devastating payload with pinpoint accuracy.

9. North American P-82 Twin Mustang

The American North American P-82 Twin Mustang was a long-range escort fighter developed to escort bombers on raids against Japan. Rather than merely making existing single-engine Mustangs longer, it put two fuselage units, fitted with complete cockpits and dual flight controls for both to assume duty, in tandem with each other across a common center wing and horizontal tail in an effort to decrease fatigue during the expected unusually long over-oceanflights that would occur in the Pacific war. This aircraft’s first flight was in June 1945 and because it was after the Second World War the aircraft never got the opportunity to be flown in to combat or to help end the world’s largest ever armed conflict; although this is a shame the P-82 did accomplish so much that it could have helped do that much sooner in other ways.

Twin Mustang’s Long-Range Strengths:

• Combined two P-51 fuselages
• Designed for B-29 escorts
• Two pilots shared duties
• Flew 5,051 miles nonstop
• Served during Korean War

The problem to which the Twin Mustang was devised. How best to adequately escort bombers over unprecedented ranges. It put immense strain on a single pilot of a conventionally configured fighter. The use of two complete cockpits and controls for both (allowing change over and weariness relief to be experienced), enabled flight at extreme range. The Twin Mustang was unable to meet its planned target use in the Second World War (the aircraft was completed just after the declaration of war’s end), and its designer found a number of post war uses for his concept.

10. Tupolev TB-3 and Polikarpov I-16 ‘Zveno’

The Soviet Zveno system carried out further experimentation that continued to develop parasite fighters by incorporating a Tupolev TB-3 heavy bomber to carry two manned Polikarpov I-16s equipped with bombs beneath the wing. This enabled the fighters’ very short range to be dramatically extended, and the TB-3 would carry its carried short-ranged I-16s part of the way towards their target destination, instead of making them embark on very short journey over vast distances on their own. The set-up allowed the fighters range and a heavier bomb load, while vulnerable TB-3 towed its “offspring” to beyond optimum radius before separating and launching the aircraft in the direction of the target away from itself. Each attacker carried out their own bomb runs and the pair then departed for base, not necessarily on common heading, apart from the TB-3 that could also proceed towards home independently. Even as the TB-3 itself was technically already outdated a few years into the war it still maintained its bombing and transport roles, in addition to being a Zveno and a light tank carrier.

Zveno System Highlights:

• TB-3 carried two I-16s
• Fighters carried bombs
• Extended short-range fighter reach
• Fighters launched near targets
• Aircraft returned separately

The Zveno system was a bold but not very successful bid to extend fighter range, while avoiding the expense of a fully new design of long-range fighter. The TB-3 was used as an air mother carrying two armed I-16 fighters in under the wings. This enabled the fighters to get to parts of targets, which would otherwise have been far out of range. An additional advantage to the arrangement was that the fighters could be armed with heavier bomb loads than they could during conventional transport flights as much of the trip could be handled by the mothership. The fighters acted in an independent attack and retraced their routes alone.