WWII Air-to-Ground Special Purpose Weapons

‘Mistel’ (mistletoe) was the name the Germans gave to their combination system whereby a fighter aircraft was attached to an old bomber loaded with explosives. The fighter, in this case an Me 109, flew its charge to the target, broke contact and guided the bomber to impact by radio control.

The ‘Weary Willie’ idea of packing old B- 17s with explosive and crashing them on to a target was abandoned in favour of more modest plans involving these Grumman F6F Hellcats. Too late for service in 1945, they saw action in the Korean War.

The Förstersonde consisted of a pair of 77-mm recoilless guns mounted vertically in the wing of an FW 190 and triggered by the electro-magnetic field created by the mass of metal in a tank. It was successful in penetrating the armour of a captured T-34 tank. Very little is known of this project except that trials were made in early 1945 on the fire control system which proved that it was feasible if not immediately perfect, but the weapon never got into service.

Many of today’s air-to-ground weapons can trace their ancestry back to munitions designed in World War II. Most nations experimented with guided weapons, the Germans deploying some to great effect. There were also unique ideas such as the Dambusters’ ‘Bouncing Bomb’ produced for special operations.

Weary Willie and ‘ Tired Tim’ were a couple of much-beloved strip cartoon characters in the days before World War IL , and it was probably the America custom of describing time-expired operational airframes as ‘war weary’ that led to the name Weary Willie for the Boeing B-17s modified for remote-control crashing onto targets such as the underground lairs (No-ball targets) of weapons like the V-1 flying bomb . The relegated bombers were never in the event used for such work, but would have been packed with explosive and taken under radio control on their last mission.

But if such outsize flying bombs as these represent the larger of the special purpose weapons, the other end of the scale is surely and ably represented by the tiny Razzle (and the larger Decker). These were incendiary devices intended for use against enemy crops and forests and consisted of a small piece of wet cotton wool wrapped round a phosphorus pellet and enclosed within two sheets of celluloid about 7.6 cm (3 in) square. Some 450 such devices were carried in a drum of liquid and dropped over enemy territory, to lay on the ground undetected until they dried out and ignited

Yet undoubtedly the most famous special device of the entire conflict is the cylindrical bomb used to destroy the vital Ruhr dams.

Simple in concept, this Barnes Wallis design was little more than a cylinder, set spinning by means of a VSG Hydraulic motor via a ‘V’ belt. With 2994 kg (6,600 lb) of RDX explosive making up, the greater part of the 4196 kg 2994 kg (9,250 lb) total the bomb was capable of skipping total the over the protective booms at 500 rpm once released by the parting of the pair of suspended trusses, to sink against the target wall and be fired by the hydrostatic fuses set to operate at a depth of 9.14 m (30 ft).

Another special Weapon of similar concept was that intended to sink the Tirpitz. This preceded the larger bomb, and was codenamed ‘Highball’. Of spheroidal shape, it was intended to be carried in pairs by an adapted de Havilland Mosquito. The delivery journey and dash back to base would be carried out at 4572-m (15,000-ft) altitude which, although probably alerting the enemy radar, would permit an enhanced range and improved flexibility of the actual attack. Unfortunately all came to naught although tests had been satisfactorily concluded, political pressures finally winning the day so that not even the squadron of special Mosquitoes despatched to operate against the Japanese fleet was ever used.

The supply of special weapons was not in any measure confined to the Allies. For example , the Luftwaffe boasted that its largest convention 5,511-lb SC 2500 nicknamed ‘Max’ which was 3.895 m ( 12 ft 9.3 in ) long and had a diameter of 0.829 m (2 ft 8.6 in), was too large to fit in the internal bay of any German bomber and thus had to be carried externally.

One of the special weapons associated with the night raids against the UK was that popularly known as the ‘land mine’. This was an adapted device that was commonly spoken of in some awe because of its high blast effect; this was partly the result of the weapon’s lack of penetration, since it was dropped under a large parachute of coarse green material secured to the thin-walled casing with plaited lines some 12.7-mm (0.5- in) thick. These weapons were frequently dropped in company with a percentage of ‘oil bombs’, fire-raising devices distinct from the normal thermite incendiaries of which an explosive version was introduced. The oil bombs carried both fuel-oil and phosphorus within a single casing. Another contemporary special weapon was the so-called Molotov cocktail, which consisted in the main of a high-explosive bomb with an attached container for conventional incendiaries which opened before making impact and thus scattered its load.

But perhaps the most dangerous special weapon to come from the German aerial armoury was quite small, the ‘butterfly-bomb’ or SD-2 which consisted of a cylinder no more than a few centimetres in diameter. Semi-circular wings so that the bomb spun to the ground in the manner of a sycamore seed. These weapons proved particular value against soft-skinned vehicles or troops in the open, detonation taking place on impact or after a delay; the weapons could also act as ‘booby-traps’, lying in undergrowth etc. until disturbed. Fighters or Junkers Ju 87s could lay a trail of up to 96 of these SD-2s, while twin-motor bombers could deposit some 360, a contrast in size and scope with such special weapons as the explosive-laden Grumman F6F Hellcats earmarked to fly unmanned against targets in the Pacific area.

Mistel

Without doubt, though, the glide bomb to end all glide bombs was Mistel (`Mistletoe’). It is said that this idea was put forward by the chief test pilot of the Junkers company in 1941 as a method of putting war-weary Ju 88 bombers to some practical use. In the 1930s Britain’s Imperial Airways had proposed an air mail service on the Atlantic and other routes by using a seaplane mounted on top of a flying-boat. The flying boat took off, carrying the seaplane, transported it some distance along its route, and then the seaplane released itself and flew off to continue the trip while the flying boat returned to base. The object was to use the greater power of the flying boat to get the heavily laden (with fuel and mail) seaplane into the air, as well as carry it some distance without using any of its fuel.

The proposal that now came forward in Germany was a reversal of this. The Ju 88 bomber was stripped of its interior fittings and had the cockpit space filled with a gigantic shaped charge weighing about 3,500kg. A fighter aircraft was attached above the bomber and the controls connected. All engines were started and the fighter pilot flew the combination off. On approaching his target he put the whole combination into a dive calculated to deliver the bomber to the target, then disconnected himself. He then flew an accompanying course, correcting the bomber’s flight by radio until he had steered it into impact with the target, after which he flew home satisfied with a job well done.

As might be imagined, such a revolutionary concept in 1941 was promptly thrown out, but in 1942 it re-appeared but as a means of lifting a glider into the air and then releasing it. This appeared to work successfully, then somebody in the Reichsluftministerium remembered the fighter/bomber combination and brought the idea forward again. In 1943 it was put into development and a combination Ju 88A/Messerschmitt Bf 109 flew a series of tests, leading to an order for 15 sets to be built under the code-name Beethoven. The shaped-charge warhead was built and tested, first against a redundant French battleship and then against reinforced concrete, against which it could defeat 18 metres thickness.

Once the design was perfected and made operational, it became Mistel 7, and the machines were operated in 1944 from a base in France against Allied shipping in the Bay of Biscay. It is reported that several hits were made, though no ship was sunk as a result. Now a crash programme was begun to assemble 100 units, to be called Mistel 2, which were to be used in Operation Iron Hammer against the advancing Allied forces nearing Germany. The order was then increased to 250, and several other combinations of fighter and bomber, according to what machines could be rounded up and converted, were put in hand, but, as with so many other last-minute schemes, the war ended before the force could be built and assembled.

Gliding Torpedoes

Blöhm und Voss, being primarily a firm with naval interests, became involved in the development of a gliding torpedo in the middle 1930s. Dropping torpedoes from aircraft was by that time a commonplace, but it was a rough and ready technique which simply took a standard naval torpedo and dropped it in the water from as low as the pilot dared to go. The Blöhm & Voss Luft-Torpedo (LT F5b) began with a standard 750 kg fleet torpedo and added tail surfaces and apparatus for setting the steering and depth controls from the aircraft. This worked well and improved the accuracy of the aviators, and it was followed by the LT 10 Friedensengel (Angel of Peace’) which used the same torpedo but added wings and tail-planes so that it could make a long glide before entering the water at the proper speed and angle. About 450 of these appear to have been manufactured during the war years, though accounts of their employment are certainly very scarce. Production was halted in 1944 and changed to the LT 11 or Schneewittchen (`Snow-white’), a rather more advanced model, but few of these were ever made.

The German bouncing bombs

There was an immediate response to the bomb by the Germans. After the Lancaster crashed from hitting high-tension power lines, the intact mine was removed from the wrecked plane by the local troops, who initially thought that it was a reinforced auxiliary fuel tank. Once its true nature was realized it took just ten days for the German engineers to draw up detailed blueprints of all the design features and they set out to build a bouncing bomb of their own. The first constructed was code named Kurt and was a 850lb (385kg) bomb built at the Luftwaffe Experimental Centre in Travemünde. The initial trial was from a Focke-Wulf Fw-190 but the importance of backspin was not recognized by the designers, and the bomb leaped high in the air after release, posing a danger to the aircraft.

To obtain more range, and thus provide safer conditions for the dropping aircraft, which, it appeared, would usually be above the bomb when it detonated, a rocket rail unit was fitted. This increased the range but also showed a tendency to push the bomb off course if it happened to be yawing at the instant of ignition. To cure this a gyroscope stabilising unit was designed, which would have been run up before the bomb was dropped but while the aircraft was aimed at the target, and which would subsequently detect any tendency to veer off-course and apply the necessary corrections to the tail unit to steer it back again. But, in November 1944, before this could be built and tested, the project was closed down. The one thing that remains to be discovered about Kurt is what target the Luftwaffe planned to use it against?

The fact that the Germans found an intact bomb was due to a vital factor overlooked by the British designers. As we have seen, these were essentially mines fitted with depth charges. The bomb that overshot – because it was never immersed in water – was never going to explode, and so it was recovered intact. A conventional time fuse should have been fitted, and then the weapon would have functioned as conventional bomb if it overshot the dam. And the Germans missed something equally crucial – the fact that the bombs were spinning. It was the backspin that gave the bouncing bombs their awesome ability to ricochet so far across the water. This remained a military secret long after the war; indeed, you will note that there is no mention of spin even in the movie of the Dambusters. Although Barnes Wallis advised on the film, and it is painstakingly accurate in many respects, he was prohibited from releasing this vital piece of information and the public never knew.

The drawings and diagrams were ultimately all lost, and little technical detail remained. In 2011 Ian Duncan, a director with the British documentary company Windfall Films, recreated a scaled-down version of the bouncing bomb, with Dr Hugh Hunt of Cambridge University in charge of the experiments. They began logically (as did Barnes Wallis) with small spheres leading onto increasingly large projectiles, ending up with a half-size bouncing bomb with which they successfully targeted a purpose-built dam. The physics proved interesting: just as Barnes Wallis had calculated, the lower the bomb was dropped, the further it travelled.

The Americans had tried to make use of this principle immediately after World War II. Because they were sent every British military secret, their designers were aware of the need for backspin, and they also knew that a low launch altitude helped maximize the trajectory of the spinning mine. They copied the British design of the Highball weapon, renaming it Baseball. Initial investigations were promising, so – to maximize the distance the bomb would travel – they decided to launch it at 25ft (7.6m), less than half the altitude of the British Dambusters. This was such a success that the officials reckoned the pilot should fly even lower and see how far the bomb went this time. As the plane sped above the water at the perilously low level of 10ft (3m) the bomb was dropped and bounced perfectly – so much so that it smashed up through the fuselage, completely severing the aircraft’s tail. The plane flew on momentarily and then smashed into countless fragments as it hit the water at speed. The surviving film of the incident makes the whole event so obviously predictable, and one can only sympathize with the compliant pilot who either thought it would be good idea at the time or was simply following orders.

Meanwhile, Guy Gibson’s 617 Squadron remained together and they were subsequently given the opportunity to deliver Barnes Wallis’s later weapons. The Cookie 5-ton bomb was carried by Lancaster bombers and used with great effect to attack submarine pens in France and German warship bases in the fjords of Norway. Although it proved a success, it was no more than a vast, conventional blast bomb. Barnes Wallis had in mind a very different secret weapon which would penetrate the ground and deliver such powerful shockwaves that it would bring down buildings and bunkers for a considerable distance around. Whereas a conventional bomb (no matter how large) did its damage through air-blast, Barnes Wallis’s revolutionary new bomb would generate a miniature earthquake, by setting up huge ground waves of energy. These could demolish a building from below.

Other solutions were sought to increase the penetrating power of high-explosive bombs. Towards the end of the war, a rocket-assisted high-impact bomb was conceived by the Royal Navy’s Captain Edward Terrell as an alternative answer. The rocket could give a smaller bomb the velocity needed to penetrate thick concrete. The weapon weighed only 4,500 lb (2,000 kg) and could be dropped from a safe altitude of 20,000 ft (about 6,000 m). When it had descended to 5,000 ft (1,500 m) a barometric fuse would fire a rocket motor in the tail. This accelerated the bomb to give it a final speed of 2,400 ft/s (730 m/s). This secret weapon was first carried under the wings of B-17 Flying Fortress bombers used by the 92nd Bomb Group on 10 February 1945 against the S-boat pens at IJmuiden, Netherlands. Altogether, 158 of these so-called Disney bombs were used operationally by the end of the war in Europe.

Barnes Wallis scaled down his proposals for his gravity-assisted penetrating bomb, and in 1944 designed instead the 12,000 lb (5,400 kg) Tallboy bomb, which could be carried by the current bombers. Later in the war, the Avro Lancaster improved to such an extent that it could just support a 10-ton payload and so, as we shall see, the 22,000 lb (10,000 kg) Grand Slam bomb was finally put into production. It was a secret weapon of unprecedented power. As in the case of the Tallboy bomb, the Grand Slam was spin-stabilized by its fins and was built with a thick, heavy steel case to allow it to penetrate deep layers of the ground unscathed. Dropped from high altitude, it would impact at nearly the speed of sound. During manufacture, hot liquid Torpex explosive was poured in to fill the casing and this took a month to cool down and solidify. Torpex (named because it had been developed as a TORpedo EXplosive) had more than 150 per cent the force of TNT. The finished bomb was so valuable that aircraft that could not drop their weapon in an abortive mission were ordered to return to base and land with the bomb intact, instead of jettisoning it over the open sea. Barnes Wallis had planned to create a 10-ton weapon in 1941, but it was not until June 1944 that the bomb was ready for use. It was first dropped on the Saumur rail tunnel from Lancaster bombers of 617 Squadron. No aircraft were lost on the raid, and one of the bombs bored 60 ft (18 m) through the rock into the tunnel, blocking it completely. These massive ‘earthquake’ bombs were also used on the great concrete structures that the Germans were building to protect their rocket storage bunkers and submarine pens, and caused considerable damage. The Valentin submarine pens at Bremen, Germany, were made with reinforced concrete roofs some 23 ft (7 m) thick yet they were penetrated by two Grand Slam bombs in March 1945.

Ultimate penetration bombs

These ground-penetrating bombs are among the secret weapons that have gone on to give rise to present-day developments. Remote guidance was added to the Tallboy bomb by the United States during the Korean War. The resulting weapon was the 12,000 lb (5,400 kg) Tarzon bomb, used with devastating effect against a deep underground control room near Kanggye. Bunker buster bombs were also dropped at the Ali Al Salem Air Base, Kuwait, in 1991 as part of Operation Desert Storm. At the outbreak of the First Gulf War none of the NATO forces possessed such a weapon, so some of the original Barnes Wallis bombs were brought out of museums and used as templates for the construction of 2-ton bombs. They were laser guided by the United States forces and proved highly effective.

During the late 1990s a nuclear bomb was being designed by the United States for use in tactical warfare. Known as the Robust Nuclear Earth Penetrator it underwent extensive design and development even though the use of nuclear weapons was prohibited by international agreement. Work on the project continued until it was finally cancelled by the Senate in 2005. Meanwhile, in 2007 the Boeing Company announced that they had carried out successful tests of their Massive Ordnance Penetrator (MOP) weapon at the White Sands Missile Range, New Mexico. This bomb, also known as the Big Blu and Direct Hard Target Strike Weapon, is a 30,000 lb (14,000 kg) penetration bomb designed to be delivered by a B-52 Stratofortress or a B-2 stealth bomber against heavily protected subterranean targets. This is a project for the United States Threat Reduction Agency, and is designed to hit the ground at supersonic speeds so that it can penetrate deeply prior to detonation. Most of the mass is in the casing, not the explosive component. All of his stems from the work of Barnes Wallis during World War II, so once again the legacy of these secret weapons remains with us to this day.

USA guided missiles

One of the first guided missiles designed in the United States was the Dragon, a radio-controlled aerial torpedo with a television camera mounted in the nose. Development proved difficult, however, when private television and electronics related firms attempted to merge their designs with the air- frames developed by the military. To overcome some of the ensuing technical difficulties involved in systems integration, the NDRC enlisted the aid of the National Bureau of Standards, which formed a special research group for the project. But before development advanced to the production stage, the project became sidetracked when the navy requested the National Bureau of Standards to design an effective antisubmarine guided missile. Using a scaled- down version of the Dragon, late in 1944, the National Bureau of Standards produced the Pelican, a radar-guided antisubmarine missile.

By this time, however, the German U-boat threat had subsided greatly, and despite its excellent performance in flight tests, the navy scrapped the Pelican, declaring that the missile was of “no operational use.” The technical knowledge gained from the development of the Pelican was subsequently applied to a more advanced model, the SWOD Mk 9 air-to-surface guided missile, also known as the Mk 57 Bomb, or Bat. The Bat, developed by the Navy Bureau of Ordnance in cooperation with the Radiation Laboratory at MIT, was a low- angle glide bomb equipped with a radar bombsight for active homing. The Bat entered service in January 1945 and was first used on 23 April 1945 at Balikpapan, Borneo. Although the Bat was the only completely automatic target- seeking missile developed during the war, its efficacy in combat proved less than satisfactory.

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