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A glide bomb or stand-off bomb is a Standoff missile with flight control surfaces to give it a flatter, gliding flight path than that of a conventional bomb without such surfaces. This allows it to be released at a distance from the target rather than right over it, allowing a successful attack without exposing the launching aircraft to anti-aircraft defenses near the target. Glide bombs can accurately deliver in a manner comparable to at a fraction of the cost—sometimes by installing flight control kits on simple —and they are very difficult for surface-to-air missiles to intercept due to their tiny and short flight times. The only effective countermeasure in most cases is to shoot down enemy aircraft before they approach within launching range, making glide bombs very potent weapons where wartime exigencies prevent this.
World War II-era glide bombs like the German Fritz X and Henschel Hs 293 pioneered the use of remote control systems, allowing the controlling aircraft to direct the bomb to a pinpoint target as a pioneering form of precision-guided munition. Modern systems are generally self-guided or semi-automated, using GPS or to hit their target.
The term "glide bombing" does not refer to the use of glide bombs, but a style of shallow-angle dive bomber.
Siemens-Schuckertwerke was already occupied with remote controlled boats (the or Fernlenkboote), and had some experience in this area. Flight testing was performed under the supervision of an engineer called Dorner from January 1915 onwards, using airships as carriers and different types of biplane and monoplane glider airframes to which a torpedo was fitted. The last test flight was performed on February 8, 1918.
It was planned to use the Siemens-Schuckert R.VIII bomber as a carrier craft, but the Armistice stopped the project.
The German solution was the development of a number of glide bombs employing radio control guidance. One was created by fitting a control package on the rear of an otherwise standard bomb, starting with their 1400 kg armor-piercing bomb to create the Ruhrstahl SD 1400, commonly referred to as Fritz X. This weapon was designed specifically to pierce the deck armor of heavy cruisers and battleships. The bomb aimer dropped the bomb from high altitude while the aircraft was still approaching the ship, and guided it to impact with the target by sending commands to spoilers attached to its rear. This proved to be difficult to do, because as the bomb dropped toward the target it fell further behind the launch aircraft, eventually becoming difficult to see. This problem was solved by having the launch aircraft slow down and enter a climb to avoid overtaking the bomb as it fell.
In addition it proved difficult to properly guide the bomb to impact as the angle of descent changed, and if the bomb was not aimed accurately so as to end up roughly right over the target, there was little that could be done at later stages to fix the problem. Nevertheless, the Fritz X proved useful with crews trained on its use. In test drops from , experienced bomb aimers could place half the bombs within a radius and 90% within .
Design work started as early as 1939, and a version of the guidance package mounted to standard 500 kg bombs was tested in September 1940. It was found that the bomb was unable to penetrate a ship's armor, so changes were made to fit an armor-piercing warhead before the system finally entered service in 1943. The basic A-1 model was the only one to be produced in any number, but developments included the B model with a custom armor-piercing warhead, and the C model with a conical warhead which was designed to hit the water short of the ship and then travel a short distance underwater to hit the ship below the waterline. The guidance system for the Hs 293 series was the same as the Fritz-X unpowered munition; it used a Funkgerät FuG 203 Kehl radio control transmitter with a single two-axis joystick in the deploying bomber, and an FuG 230 Straßburg receiver in the munition.
A more widely employed weapon was the Henschel Hs 293, which included wings and a rocket motor to allow the bomb to glide some distance away from the launch aircraft. This weapon was designed for use against thinly armored but highly defended targets such as convoy merchantmen or their escorting warships. When launched, a small liquid-fueled rocket fired to speed the weapon up and get it out in front of the releasing aircraft, which was flown to approach the target just off to one side. The bomb then dropped close to the water and glided in parallel to the launch aircraft, with the bomb aimer adjusting the flight left or right. As long as the bomb was dropped at roughly the right range so it did not run out of altitude while gliding in, the system was easy to use, at least against slow-moving targets.
The Hs 293 was first used operationally in the Bay of Biscay against RN and RCN destroyers, sloops and frigates. Its combat debut was made on August 25, 1943, when the sloop HMS Bideford was slightly damaged by a missile which failed to fully detonate, but killed one crewman. Another sloop, HMS Landguard, survived a near miss with slight damage. The Germans attacked again two days later, sinking HMS Egret on August 27, 1943; they also seriously damaged HMCS Athabaskan. Over one-thousand Allied soldiers died on 25 November 1943 when a Hs 293 sank the troopship from Mediterranean KMF convoys.
American, British and Canadian scientists also developed sophisticated radio jamming to disrupt the guidance signal. Ultimately nine different jamming systems were deployed in the European theater against these weapons. While early models proved inadequate, by the time the Allies were preparing for the invasion of France in 1944 more capable systems were deployed, and the success rate of guided weapons declined considerably. Even more important to the defeat of the weapons was Allied command of the airspace and the interception of incoming bombers by Allied fighter aircraft.
The Hs 293 was also used in August 1944 to attack bridges over the Sée and Sélune at the southern end of the Cherbourg peninsula in an attempt to break US general Patton's advance, but this mission was unsuccessful. A similar mission against bridges on the river Oder, designed to slow the Soviet advance into Germany, was made in April 1945 but failed.
The Germans also experimented with television guidance systems on the Hs 293D models. The use was problematic – as the bomb approaches the target, even tiny amounts of control input would cause the target to jump around the TV display, so much of the difficulty was in developing control systems that would become progressively less sensitive as the pilot required. A wire-guided version was also developed, but this Hs 293B variant was never deployed.
The first to be used operationally was the Aeronca GB-1, essentially an autopilot attached to a small glider airframe carrying a bomb. It was intended to allow the 8th Air Force bombers to drop their payloads far from their targets and thus avoid having to overfly the most concentrated areas of anti-aircraft artillery fire. It was first used on 28 May 1944 against the Eifeltor marshalling yard in Cologne, but only 42 of 113 bombs released reached anywhere near the target; most "spun in and exploded 15 miles from the target... many of the batteries failed to hold their charge").
More advanced models in the GB series included the television guided GB-4, GB-5, GB-12, and GB-13, which used contrast-seekers for anti-ship use, and the command guidance GB-8, 'Azon', 'Razon', as well as the Infrared homing 'Felix'. US Navy glide bombs included the 'Bat' and its earlier variant, the 'Pelican'. The longer-range Bat used an active radar seeker and was used in the Pacific on August 13, 1944, but could not distinguish between targets in a cluttered environment and could be easily spoofed by even simple radar countermeasures. Only four examples of an experimental glide bomb, the 'Pratt-Read LBE', were produced.
In the anti-ship role, direct attack from an aircraft even at long range became more dangerous due to the deployment of anti-aircraft missiles on ships. Weapons such as the Bat had ranges too short to keep the attacking aircraft out of range, especially in a force provided with air cover. This was addressed with the introduction of small jet engines that greatly extended the range, producing the anti-shipping missile class that remains widely used today.
Similarly, the need to attack well-defended targets such as airbases and military command posts led to the development of newer generations of glide bombs. European air forces use a glide package with a cluster bomb warhead for remotely attacking airbases. Paveway and JDAM are used.
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