* Once air forces became serious users of using dumb bombs, they started looking for ways to make them more accurate, or in modern terms "smarter". The first efforts along this line took place in World War II, in the form of guided "glide bombs" that could allow a bomber to accurately strike a target from a distance that would keep it out of range of the target's air defenses. This chapter discusses glide bombs developed by Germany, Japan, and the Soviet Union.
* The Germans experimented with glide weapons as far back as the First World War, in the form of "glide torpedoes" designed for the Imperial German Navy by Siemens-Schukert Werke (SSW). These were very ingenious weapons, featuring a "wire guidance" system that allowed an operator to control their flight via wires trailing behind them, and an airframe that split open to release the torpedo. Both biplane and monoplane glide torpedoes were developed, with weights of up to a tonne. While some test drops were performed from Zeppelins and captive tests were performed with bombers, these weapons were not used in combat during the war.
Glide torpedoes were developed for the Third Reich in the late 1930s by the Blohm und Voss company. The sketchy information available indicates that they were unguided after launch, and saw little or no combat.
Blohm und Voss also experimented with a "glide torpedo" that was actually a very primitive attempt to build the equivalent of a modern "sea skimmer" antiship missile. This weapon, designated the "BV-143", was designed to glide down to wavetop height, where it would use a mechanical "feeler" arm about two meters long to gauge its altitude over the waves. On contact with the waves, the feeler arm would fire the weapon's liquid fuel rocket engine to keep the weapon at altitude until it struck the target ship above the waterline. BV-143 prototypes were launched four times, and to no surprise all of them went into the water. Sea skimmers would have to wait for better technology.
* Blohm und Voss also developed a true glide bomb named "Hagelkorn (Hailstone)", designed by Dr. Richard Vogt. This was a streamlined bomb with a cruciform tail and long slender wings, with the wings made of steel cores supporting an airfoil of form-cast concrete, presumably with some sort of reinforcement to keep it from cracking under flexure. This unusual construction was apparently intended to help separation of the weapon from the carrier aircraft. When the Hagelkorn was attached to the carrier aircraft's stores rack or pylon, stubs were fitted between the aircraft and the tips of the Hagelkorn's long stiff wings to cause a slight bend. The spring tension provided by the concrete-stiffened wings ensured clean separation.
The initial version of the Hagelkorn was the "BV-226", which had a spindle-shaped body 3.53 meters (11 feet 7 inches) long, with long slender wings spanning 6.4 meters (21 feet), and a cruciform tail. The front half of the body contained a warhead, while the rear half contained the guidance system. The long wings gave the Hagelkorn a glide ratio of 25:1, meaning it flew 25 meters for every meter it dropped, and so had potentially long standoff range. The BV-226 quickly led to the "BV-246", which was similar but had a twin-tailfin configuration.
The Hagelkorn had a gyroscopic stabilization system, and it appears that at least at first that was its only guidance scheme. The weapon was simply released to glide off in the direction of the target. That was obviously not very accurate, particularly for a long-range weapon, and the Germans worked hard to develop a reliable, accurate, and jam-resistant means of providing precision guidance for the Hagelkorn, particularly against targets outside of visual range.
Designing a guided weapon that could deal with countermeasures was difficult, particularly because the British were very clever at electronically outfoxing the Germans, so much so that some Germans refused to believe the British could be so many steps ahead of them. Experiments were performed with infrared and radio guidance schemes, but the Luftwaffe was not enthusiastic about the Hagelkorn, and though over 1,100 of the weapons were built starting in late 1943, the project was canceled in early 1944. Test drops of the weapon were performed by He-111 bombers and FW-190 fighters, but the Hagelkorn saw little or no combat action.
The BV-246 was revived a year later in small-scale tests where it was fitted with a passive radar seeker, or "Radieschen", to home in on emissions from Allied radar stations. Ten of these weapons were tested, and though two proved extremely accurate, the other eight failed. There was no time left for the Reich to field such a weapon in any case.BACK_TO_TOP
* The Germans were much more enthusiastic about the development of two other guided munitions, the Henschel "Hs-293A" and Ruhrstahl "Fritz-X" glide bombs. This section focuses on the Hs-293A, with the next discussing the Fritz-X.
The motivation for developing these guided weapons was attacks on naval vessels. Hitting a moving target like a ship from an aircraft is obviously much more difficult than hitting a fixed target on the ground. Of course, scoring a hit becomes easier the closer an aircraft gets to the ship, but as the saying goes: "If the enemy is in range, so are you." The closer an aircraft got to a ship, the better a target it became for ship's antiaircraft (AA) guns.
This problem was aggravated if the target was, for example, a heavily armored battleship. A conventional bomber had to attack such a monster from the air with armor-piercing bombs dropped from high altitude to give them the kinetic energy needed to punch through the target's armor before exploding, but that made hitting the target difficult.
The alternate approach was the dive bomber, in which a pilot flew his aircraft flew directly down at the target at a steep angle, building up speed and ensuring accuracy through the simple measure of aiming his entire aircraft at the target, and releasing the bomb at low altitude. This put the dive bomber into the teeth of AA guns, and such aircraft also had to stand the stresses of screaming dives and the resulting high-gee pull-outs. That meant they could not be very big, and so in general could not have the long range needed for an ocean-patrol aircraft. Naval dive bombers were carrier aircraft, and the Germans never had an operational aircraft carrier.
Torpedo bombers had similar limitations. Dropping a torpedo from an aircraft was a somewhat tricky business, and it was difficult for an aircraft to carry a torpedo big enough to sink a large vessel with a few hits. Torpedo bombers were also vulnerable to AA fire while they made their torpedo drops. The skip bombing tactics used by the Americans in the South Pacific suffered some of the same drawbacks.
While dive, torpedo, and skip bombing were all used effectively by other nations, the Germans decided to pursue another option for antiship attack, one that would win out, decades later: guided weapons. Electronic guidance would allow the launch aircraft to release the weapon out of range of target defenses, and then direct it to a pinpoint strike on the target.
* A team at Henschel under Dr. Herbert Wagner began work on the Hs-293 in July 1940. Wagner and his team built a number of "Hs-293V-1" prototypes. These were unpowered glide bombs. They were tested successfully, and followed by a number of similar "Hs-293V-2" and "Hs-293V-3" prototypes, with minor refinements. However, the tests proved that an unpowered glide bomb tended to fall behind the launch aircraft, making it difficult to guide, and so the next version, the "Hs-293A-0", had a pod strapped underneath its body containing a Walter 109-507B liquid-fuel rocket motor. Results were very satisfactory, and with a few further changes the weapon went into production as the "Hs-293A-1".
The Hs-293A-1 was a radio-guided glide bomb with light alloy wings spanning three meters (ten feet) and tail surfaces of similar construction. While early units used conventional elevators and ailerons for control, production weapons used spoilers. There was no rudder; the bomb turned by banking.
The Walter rocket was powered by a fuel known as "Z-stoff", which was a water-based solution of sodium permanganate or calcium permanganate, and an oxidizer known as "T-stoff", or concentrated hydrogen peroxide -- a fluid that is, incidentally, unstable, corrosive, and in general extremely nasty to handle. The Z-stoff was actually a catalyst that promoted the breakdown of the hydrogen peroxide into steam. The rocket motor could provide 5.9 kN (600 kg / 1,320 lb) of thrust for ten seconds. A flare was fitted to the tail of the Hs-293A to allow the operator to track its flight, after tests demonstrated it was hard to see the weapon at long range under conditions of poor visibility.
The warhead was based on the standard 500 kilogram (1,100 pound) SC500 high explosive bomb. The SC500 was not an armor-piercing bomb; the Hs-293A was intended for attacks on merchant vessels and other unarmored ships. The forward part of the Hs-293A's fuselage consisted of the warhead, while the rear part contained the control electronics and batteries. The fuselage was 3.82 meters (12 feet 6 inches) long, and the entire weapon weighed 1,045 kilograms (2,300 pounds).
The production Hs-293A was controlled by the "Kehl-Strassburg" superheterodyne command and control system, with the Kehl transmitter unit in the launch aircraft and the Strassburg receiver system in the glide bomb. The bomb could be preset to one of 18 different frequencies in the 48:50 MHz band to allow up to 18 bombers to each drop and control a glide bomb simultaneously. The operator guided the bomb with a joystick wired to the Kehl transmitter. The first aircraft fitted to carry the Hs-293A was the Dornier Do 217. Eventually the weapon was also carried by the Heinkel He-111 or He-177, the Focke-Wulf FW-200, and (in a pinch) by other types.
In operation, the carrier aircraft generally carried two Hs-293As, one under each wing. Engine exhaust was piped into the bombs to keep the propellants from freezing. On release, the flare in the tail of the bomb and the booster rocket were ignited. The operator tracked the bomb by watching the tail flare, and used the Kehl unit's joystick to keep the bomb lined up on the target. Depending on glide angle, the bomb could reach terminal velocities of 435 to 900 KPH (270 to 560 MPH). With release from an altitude of 1 kilometer (3,280 feet), the Hs-293A could glide as far as 11 kilometers (6.8 miles).BACK_TO_TOP
* Work on the Fritz-X proceeded in parallel with work on the Hs-293. Fritz-X was also known as the "FX-1400" or "X-1" by the manufacturer, Ruhrstahl AG, and "PC-1400X" by the German Air Ministry (Reichsluftfahrtministerium / RLM). The Fritz-X was designed by a team under Dr. Max Kramer of the German Aviation Research Institute (Deutsche Versuchsansalt fuer Luftfahrt / DVL), beginning in 1939. Like the Hs-293A, the Fritz-X did not reach operational status until the summer of 1943.
The Fritz-X had some technology in common with the Hs-293, but it had a completely different configuration. The Fritz-X was based on the 1,400 kilogram (3,090 pound) PC1400 hardened armor-piercing bomb. The Fritx-X was 3.26 meters (10 feet 8 inches) long and weighed 1,570 kilograms (3,461 pounds). There were four stubby fixed wings arranged in a cruciform pattern around the bomb's center of gravity, giving it a wingspan of 1.35 meters (4 feet 5 inches). The Fritz-X had a steeper glide angle and so shorter range than the Hs-293A.
The box-shaped 12-sided tail framed vertical and horizontal fins. The fins had spoilers mounted on them to provide aerodynamic control, with the fins actuated by solenoids to pop them in and out of the airstream at a rate of ten times per second. The bomb was directed by a Kehl-Strassburg system like that used with the Hs-293A, and also had a internal gyro system to keep it from rolling. The Fritz-X did not have a boost motor, but a tracking flare was fitted in the tail.
The Fritz-X was carried by Dornier Do-217 and Heinkel He-177 bombers. A Do-217 could only carry one Fritz-X, in contrast to two Hs-293As. A total of about 2,000 Fritz-X bombs was built, with 200 used in combat. Further work focused on development of a wire-guided version and then a spin-stabilized version, but these efforts were canceled, since increasing Allied pressure on Germany meant that more emphasis had to be placed on defensive rather than offensive weapons.BACK_TO_TOP
* Luftwaffe aircraft armed with these glide bombs went into combat at the end of August 1943, attacking Allied shipping in the Bay of Biscay. On 25 August 1943, they sank the escort sloop HMS EGRET and badly damaged the destroyer HMCS ATHABASCAN. These attacks were among the first recorded instances of operational use of guided weapons. The British Admiralty ordered their warships to stay at least 320 kilometers (200 miles) from the French coast until countermeasures could be devised.
The glide bombs were used more intensively in the Mediterranean, with spectacular results at first. Late on 8 September 1943, the terms of Italy's armistice with the Allies went into effect, and the Italian fleet left their anchorage on the Italian mainland, bound for Malta, where the ships would be surrendered. The Italians told the Germans that the fleet was going to sea to help fight the Allies, but the Germans were suspicious, and Luftwaffe aircraft shadowed the warships to see where they were going.
The next day, as the fleet passed through the Straits of Bonafacio, which separates Corsica from Sardinia, it was attacked by 11 Do-217s carrying Fritz-X glide bombs. The bombers concentrated their attacks on the large modern battleships ROMA and ITALIA. The ROMA was hit twice, bringing it dead in the water while fires raged below decks. Twenty minutes after the first hit, the fires reached the ROMA's magazines, the resulting explosion breaking the ship in half; it folded up and sank with most of her crew. The ITALIA was hit by a single Fritz-X, but although the battleship took on water, it managed to limp to Malta.
That same day, the Allies landed on the beach at Salerno to begin their movement into Italy. The Luftwaffe responded with a week of glide bomb attacks, badly damaging the battleship HMS WARSPITE, the cruisers HMS UGANDA and the USS SAVANNAH, and sinking or damaging several other lesser vessels. The WARSPITE was hit by three Fritz-X bombs, one of which penetrated six decks and blew a hole in the ship's bottom. The ship took on a good deal of water and was completely disabled, but fires didn't break out and casualties were only 9 dead and 14 wounded, blessedly light for such a beating. The battleship was towed away and did not return to action until June 1944.
* The Luftwaffe also mounted a number of raids in October and November 1943 against Allied convoys in the Mediterranean, using Hs-293As to attack escort vessels so the merchantmen could be struck by torpedo-carrying Ju-88 bombers. However, the days of the Luftwaffe's success with the glide bombs were short-lived. Allied air superiority was steadily growing, and when the Allies landed at Anzio in January 1944, German bombers encountered fierce fighter opposition and suffered badly, though they did sink the cruiser HMS SPARTAN.
The Allies also introduced electronic countermeasures against the Kehl-Strassburg control system. One system was a broadband jamming transmitter that simply disrupted the control transmission with radio noise. Another system was subtler, "spoofing" the bomb by sending false control signals to the Strassburg controller that slammed the weapon's control surfaces to an extreme position, causing it to stall and tumble, or descend in an aimless spiral. When the Luftwaffe attempted to attack the Allied fleet during the Normandy landings in June 1944, they were unable to overcome Allied fighter defenses. What few glide bombs they dropped were ineffective due to jamming and spoofing. The Hs-293A and Fritz-X were no longer useful weapons.BACK_TO_TOP
* Research was conducted at Henschel to the end of the war on more advanced variants of the Hs-293. The "Hs-293A-2" was a production change on the A-1 variant, involving a spoiler control system, and the A-2 was used in action.
The success of the Allies in jamming the Kehl-Strassburg system led to the "Hs-293B", which featured the "Dortmund-Duisburg" wire guidance system. The Hs-293B had a range of range of 30 kilometers (19 miles), with wire spooling out from both the bomb and the launch aircraft. 200 Hs-293Bs were rebuilt from Hs-293A production, and were used in limited numbers in the Mediterranean by bombers flying from northern Italy at the end of the war.
Hitler had ordered that the glide bombs not be used against land targets, in fear that the Allies might be able to recover a dud and learn the secrets of the technology. With the Allies closing in, the order was lifted, and in April 1945, Hs-293Bs were used on attacks on bridges over the river Oder in vain hopes of slowing down the Soviet advance on Berlin.
* The Hs-293 was a reliable and mature weapon, so it was used as the basis for a wide range of other weapon concepts, none of which saw operation, and many of which were never more than paper projects:
Other versions studied included delta-winged weapons; a missile intended to blast apart enemy bomber formations; and next-generation supersonic missiles. These weapons were more or less "paper projects".BACK_TO_TOP
* Only the Germans and the Americans seem to have used glide weapons in combat during World War II. The Japanese Army did work on a series of air-to-surface guided weapons designated "I-GO-1", but never used any of them operationally.
The initial "I-GO-1A" was built by Mitsubishi. I-GO-1A was a radio-guided missile of partly wooden construction with straight wings and a rocket booster, intended for launch by a twin-engine bomber. Length was 5.77 meters (18 feet 11 inches), wingspan was 3.6 meters (11 feet 10 inches), and launch weight was 1,400 kilograms (3,090 pounds), including an 800 kilogram (1,765 pound) warhead. The I-GO-1A was tested in the fall of 1944, but never used in combat.
The "I-GO-1B" was a conceptually similar but smaller radio-guided weapon built by Kawasaki. The I-GO-1B had a length of 4.09 meters (13 feet 5 inches), a span of 2.6 meters (8 feet 6 inches), and a launch weight of 680 kilograms (1,500 pounds), including a 300 kilogram (660 pound) warhead. Test drops were performed in late 1944 and 180 of these weapons were built, but again none were used in combat.
The Tokyo Imperial University also experimented with an "I-GO-1C" air-to-surface missile that homed in on the sound of gunfire from naval vessels. Some tests were apparently performed in the spring of 1945, but little came of this exercise and details of this particular weapon are very unclear.
* The one Japanese air-to-surface weapon that was fielded was the notorious piloted "Oka (Cherry Blossom)" bomb, which was carried by a bomber and used three solid rocket boosters to accelerate it towards its target.
By the summer of 1944, the war was clearly going against Japan, and in desperation the Japanese military began to adopt extreme tactics, beginning with missions offering those involved little chance of survival, and then moving on to deliberately suicidal tactics. While some of the suicide tactics were dismal failures, such as the kaiten suicide minisubmarines and explosive-laden power boats, the aerial suicide corps would prove very effective in causing tremendous damage to Allied ships. The suicide pilots became known as the "kamikaze (divine wind)", after a great storm that had saved Japan from Mongol invasion centuries before.
In the summer of 1944, as such kamikaze tactics were evolving, Ensign Shoichi Ota of the Imperial Japanese Navy (IJN) proposed a suicide aircraft in the form of a rocket-boosted glider that would be launched by a twin-engine bomber. Ota worked with the aeronautical engineering staff of Tokyo Imperial University to come up with a design, which he then submitted to his superiors. Although some Japanese military commanders were appalled at the idea of ordering their men on suicide missions, Ota's idea was approved. The engineering staff at the Yokosuka Naval Aeronautical Research Laboratory worked to convert the proposal into a flying design, implementing an aircraft that was to be easily flown by a poorly-trained pilot, as well as simple and cheap to build.
The program was assigned the designation the "Navy Suicide Attacker Model 11". Initial test examples were available by end of September 1944. They were originally designated the "MXY7", but this was quickly replaced by the simple and romantic name of "Oka" -- the fleeting nature of cherry blossoms suggesting the fate of those who piloted it.
The Oka weighed 2,140 kilograms (4,718 pounds), including a huge 1,200 kilogram (2,646 pound) steel-jacketed armor-piercing warhead. The weapon was 6.07 meters (19 feet 11 inches) long, with small wings only 5.13 meters (16 feet 10 inches) long. Since the Oka was not designed to take off under its own power, a larger wing was not needed. The bomb had a twin-fin tail assembly, and three solid rockets that could be fired by the pilot singly or in combination to provide boosts during the fall to the target to evade Allied fighters or perform the terminal attack. The weapon was primarily a glider, with a normal glide slope of about 5.5 degrees.
The pilot armed the weapon after launch by pulling a handle, which activated five detonators, one in the nose of the warhead and four on the rear. Fuzing could be set for instantaneous detonation, or a delay of up to 1.5 seconds to allow the warhead to penetrate into the bowels of a ship before exploding. The cockpit included armor protection to allow the pilot to press his attack to impact in the face of antiaircraft fire.
For flight training, a glider version was built, using water ballast to simulate the weight of the warhead and rockets. When the trainee completed the training portion of the flight, he would dump the ballast, allowing the lightened glider to land safely on a skid. At first, the trainer was a single-seat aircraft, but a tandem-seat version, with separate cockpits for instructor and trainee, was planned, with the designation of "Model 43 K-1 Kai".
Even as the ten test items were being delivered, the IJN was ordering the Oka into production. A decision was made to have it manufactured at the Yokosuka Arsenal to help keep the weapon secret. Some officials also believed that civilian manufacturing firms would find the idea so shocking that they would think the Navy had gone mad -- despite stereotypes of Japanese culture in the West, the notion of kamikaze tactics wasn't something that all or possibly even most Japanese accepted as rational. A force of volunteers, designated the "Jinrai Butai (Thunder God Corps)", was organized to fly the weapons. The volunteers were screened to weed out first sons of families, only children, or men with family responsibilities. The "winners" of the selection process were then put through indoctrination and training.
The training and flight tests were conducted through the fall and into the early winter of 1944. However, deployment proved troublesome. Two batches of Okas were sent to the Philippines on carriers late in 1944, but both carriers were sunk by American submarines, along with their suicide weapons. A few Okas were eventually transported to Formosa, Okinawa, Singapore, and elsewhere in the shrinking Japanese empire.
The delays in putting the Okas into operation led to demoralization of the pilots of the Jinrai Butai, since it left them with far too much time on their hands to contemplate death. One thing that was unsettling on contemplation was the delivery system. Each Oka was to be carried into battle on a modified Mitsubishi G4M twin-engine bomber and released at high altitude. While the Oka was likely to be all but unstoppable once released, the G4M was notoriously vulnerable. Since the bombers had to fly at high altitude to launch the Okas, they would certainly be picked up by American radar and torn to pieces by American fighters. The pilots of the Jinrai Butai knew they were going to die, but they at least wanted their deaths to pay off.
The Okas finally went into service on 21 March 1945, in an attempt to attack a US Navy fleet that had been raiding the Japanese home islands. A formation of 15 G4Ms and their escorting Zero fighters were simply slaughtered by US Navy Grumman Hellcat fighters. Only a few Zeroes made it back to base to report on the disaster. US Navy pilots reported that some of the bombers they shot down seemed to be carrying some kind of winged missile.
The Okas were sent into action again when the Americans invaded Okinawa at the beginning of April. This time, the G4Ms were sent in one at a time, in unpredictable directions, and they were able to release Okas. One scored a hit on one of the main turrets of the battleship USS WEST VIRGINIA.
Allied intelligence began to understand what the Japanese were up to. They called the Oka the "Baka", Japanese for "fool", in attempt to make a joke of it, but that was just rear-area posturing; US Navy sailors found nothing humorous about enemies who were willing to kill themselves as long as they could take some Americans with them. However, the Oka proved to rank relatively low on their list of worries. Conventional kamikaze aircraft proved far more effective than the rocket bomb, the extreme vulnerability of the bombers that launched the Okas making the weapon almost more damaging to the Japanese than the Americans. While Oka attacks were performed up to the end of June, the last hit they scored was on 11 May. The mother ships failed to return from their missions about 70% of the time.
The Japanese developed an improved Oka, the "Model 22", which was about a third lighter and powered by the Tsu-11 "turbo-piston" engine -- a dubious contraption featuring a compressor driven by a four-cylinder piston engine. Most of the major combatants in the war tinkered with such piston-jet hybrids and none of them went anywhere with the concept.
In any case, the smaller Model 22 Oka was to be carried by the Yokosuka P1Y twin-engine bomber, which was much less vulnerable than the G4M and could fly higher. The Model 22 was expected to have a range of about 64 kilometers (40 miles) in operation. About 50 Model 22s were built, but none were ever used. The Japanese also considered other improved Oka versions, including one that was powered by a proper Ne-20 axial-flow turbojet derived from German BMW jet technology and catapulted from a ground launcher, but these concepts never went beyond the paper stage.
Although the kamikazes proved to be a highly effective weapon, the Oka turned out to be less a guided weapon than a misguided one. Okas were only credited with sinking one destroyer, damaging a destroyer and a minesweeper beyond repair, and damaging a half-dozen other vessels. This was an insignificant score in comparison with the total earned by the kamikazes, and certainly the Okas in no way justified the resources and effort placed into them, much less the supreme sacrifices of their pilots.
* A Soviet designer named Vladimir Vakhmistrov came up with an interesting paper design for a glider bomb in 1944. This scheme involved a twin-boom glider, with each boom tipped by a 1,000 kilogram (2,200 pound) bomb. A fighter was attached to the top of the glider on struts to provide propulsion and targeting, and the whole system took off on an undercarriage system that was to be released after takeoff. On release from the fighter, the glider would proceed to target using a gyroscopic autopilot. The scheme was never implemented, which was just as well, since gyroscopically-guided glide bombs never proved to be a very good idea.
The Soviets didn't field guided glide bombs until the mid-1950s, when they introduced two such weapons. The "UB-2F Chaika (Seagull)" was a 2,000 kilogram (4,400 pound) class weapon with cruciform delta wings and twin tailfins. An Ilyushin Il-28 Beagle bomber could carry one externally on the centerline; while the Tupolev Tu-16 Badger bomber could carry two, one under each wing. A "Tchaika-2" was developed that had a heat seeker head.
The "UB-5 Kondor" was a 5,000 kilogram (11,000 pound) weapon, and led to an improved "UBV-5" armor piercing variant. Details of the Kondor are unclear, though it likely had a configuration similar to that of the Chaika, and was certainly only carried by the Tu-16. The Chaika and Kondor saw very little service. They were clearly antiquated even when they were introduced, and the Soviets were moving rapidly to develop much better weapons.BACK_TO_TOP