Glide torpedoes / Hagelkorn
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 through 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 also 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.
Although not actually a glide weapon, 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, named 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 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 die-cast concrete!
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 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 very long range.
The BV-226 quickly led to the "BV-246", which was similar but had a twin tail configuration, using a horizontal tailplane with a vertical tailplane attached to each end.
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. This was obviously not a very accurate means of guidance, 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 extremely clever at electronically outfoxing the Germans, so much so that some Germans refused to believe the British could be so far 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 cancelled 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.
HS-293 / Fritz-X
The Germans were much more enthusiastic about the development of two other guided munitions, the Henschel "Hs-293A" and Ruhrstahl "Fritz-X" glide bombs.
These weapons were designed for 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, and of course scoring a hit becomes easier the closer an aircraft flies to the ship. However, as the saying goes: "If the enemy is in range, so are you." The closer an aircraft came to a ship, the more it was at risk from ship's anti-aircraft (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 they exploded, but this made hitting the target difficult.
The alternative 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, at releasing the bomb at low altitude. This put the dive bomber into the range 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 very 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.
The Hs-293A and Fritz-X guided glide bombs had some conceptual similarities, but little physical resemblance. The Hs-293A looked like a small airplane, while the Fritz-X looked like a bomb with fins and a box tail.
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 V-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 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 deal with. The rocket motor could provide 600 kilograms (1,320 pounds) 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) SC 500 high explosive bomb. As this 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 warm. 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 joystick to keep it 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).
Work on the HS-293A and the Fritz-X proceeded in parallel. 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, or RLM).
The Fritz-X was designed by a team under Dr. Max Kramer of the German Aviation Research Institute (Deutsche Versuchsansalt fuer Luftfahrt, or DVL), beginning in 1939. Like the Hs-293A, the Fritz-X did not reach operational status until the summer of 1943.
The Fritz-X was based on the 1,400 kilogram "PC-1400" 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, as opposed to two Hs-293As. A total of about 2,000 Fritz-X bombs were 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 cancelled, as increasing Allied pressure on Germany meant that more emphasis had to be placed on defensive rather than offensive weapons.
Luftwaffe aircraft armed with these glide bombs weapons 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.
On the next day, as the fleet passed through the Straits of Bonafacio, which separate 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, 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 so devastating an attack. 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 more subtle, "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.
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 hopes of slowing down the Soviet advance on Berlin.
Other versions studied included delta-winged weapons; a missile intended to blast open enemy bomber formations; and next-generation supersonic missiles. These weapons were more or less "paper projects".