[4.0] World War II Glide Bombs (2)

v4.0.0 / chapter 4 of 10 / 01 may 14 / greg goebel / public domain

* The US also developed guided glide bombs during World War II, though their success with the concept was limited. In general, the technology of the time wasn't really up to the job. In the 1950s work on such guided munitions was all but abandoned as the USA focused on the nuclear option, and wouldn't be revived for a decade.

VB-13 Tarzon bomb



* The technology to develop guided weapons was easily available to most of the combatants during World War II, but the Americans lagged the Germans, mostly because of official indifference. The USAAF developed three series of glide weapons:

Little information can be found on the BG weapons. The only one of the series that actually flew was the "XBG-1", which was a conversion of a Fletcher PQ-11A target drone, which itself did not reach production. The drone's engine was replaced by a 900 kilogram (2,000 pound) bomb. The glider was to be towed to the target area and released, to be guided into the target by a TV seeker. Ten XBG-1s were built, but that was the end of it. The proposed Fletcher "BG-2" and "BG-3" glider bombs didn't even reach the prototype stage.

* The GB series were winged bombs more along the lines of the Hs-293A. They were the result of a series of studies into guided weapons performed in the US in 1940 and 1941. Most of these studies went nowhere because of disinterest, or because the organizations involved knew either about aircraft or about electronics -- but not both.

The Aeronca "GB-1" project survived because of its simplicity, though "crudity" might be a better word. The GB-1 was a 900 kilogram (2,000 pound) bomb fitted with wooden wings spanning 3.66 meters (12 feet), and a twin-fin tail assembly carried on twin booms, giving it a length about as long as the wingspan. The weapon's appearance was definitely unsophisticated. The GB-1 was guided by a gyroscopic stabilization system. It was aimed by a bombardier from a distance in front of the target, and after release the bomb simply glided away in that direction.

The rationale for the GB-1 was not stand-off distance. The concept was that a glide bomb falling at a shallow angle into a target area had a high probability of hitting the side of a tall and presumably valuable structure, while ordinary bombs falling straight down hit almost anywhere within the target area. Although in hindsight the concept seems dubious, USAAF commander General Henry H. "Hap" Arnold was in a hurry, and a gyrostabilized bomb could be developed more quickly than a radio-controlled weapon.

The GB-1 was actually issued to the USAAF 8th Air Force in late 1943, with the weapons mounted in pairs on B-17 bombers, with one bomb on shackles beneath each wing. They were used in some quantity in bombing attacks on Cologne, Germany, in early 1944. Results were unsurprisingly dismal. Accuracy was poor, and a B-17 with an external bombload suffered greatly in terms of handling, range, and performance. Although about a thousand GB-1s were used in combat, the weapon was abandoned.

The Bellanca "GB-2" and Timm "GB-3" were similar 900 kilogram (2,000 pound) weapons, which were dropped at an early stage in favor of the GB-1. The GB-1 was followed by a series of variants, all built by Aeronca, of similar configuration but with different seekers and so on:

These munitions never got out of the test stage and were canceled at the end of the war, or shortly after. A "Glide Torpedo" weapon designated the "GT-1" was developed. It was basically along the same lines as the German glide torpedoes, being essentially a GB-1 with the bomb replaced by a Mark 13 air-dropped torpedo. The GT-1 trailed a small kite assembly and released the torpedo when the assembly hit the water. The GT-1 was actually used in the Pacific Theater late in the war, being delivered by North American B-25 Mitchell bombers.

GB-1 & GB-4 glide bombs, GT-1 glide torpedo

* The TV-guided "GB-4", developed directly by the USAAF, was a more refined weapon than the GB-1, with a similar configuration but cleaner implementation. It was actually used in combat, but though it had performed well in tests, for various reasons it did poorly in the field. One of the problems seems to have been the poor quality of the image returned by early TV camera tubes, which restricted operations to broad daylight, fair weather, and easily distinguished targets. Reliability of the electronics was apparently another troublesome issue. A pulsejet-powered variant, the "JB-4", was developed but never got out of the test stage.

As with the GB-1, a number of variants of the GB-4 were developed:

As with the GB-1 variants, none of these weapons got out of the test stage, and were all canceled at the end of the war or shortly afterward. A "GB-10", which was a GB-1 with a GB-4 guidance system, was considered but not built.



* The VB series munitions were in general more conceptually similar to the German Fritz-X weapon, consisting of finned bombs, and were more successful than the GB munitions. All the VB weapons were developed by the USAAF Air Materiel Command at Wright Field, Ohio.

The first eight weapons in the series, "VB-1" through "VB-8", were modified standard aerial bombs. The VB-1 was based on the standard M44 450 kilogram (1,000 pound) high explosive bomb. It was fitted with a new tail featuring a gyrostabilization system, a pair of rudders, and a tracking flare. This weapon could only be steered right and left, and so it was named "AZON", for "azimuth only". The later "VB-2" was a 900 kilogram (2,000 pound) bomb with the same guidance scheme, though apparently it was not build in large numbers. A radio control system conceptually similar to the German Kehl-Strassburg system allowed a bombardier to direct the bomb with a joystick. This radio control system had five channels, allowing five bombers to drop and control a AZON simultaneously.

Design work on the VB-1 began in the summer of 1942, but the weapon's gyrostabilization system proved ineffective, and in early tests the AZON showed a tendency to roll, making its control surfaces useless. Eventually the bugs were worked out, and test drops showed the guided bomb had between one and two orders of magnitude more accuracy in hitting targets than an unguided bomb.

These successful tests convinced USAAF officers of the merits of guided bombs. There had been considerable resistance to the idea because the AZON wasn't a "fire and forget" weapon: once dropped, the launch aircraft had to remain on course while the operator guided the bomb into the target. Since this has remained a problem through the entire history of air-launched guided weapons, it was not an unreasonable concern. Those who accepted the usefulness of guided glide bombs, on the other hand, found the restriction to "azimuth only" guidance too severe, and wanted to wait until a fully-guided next generation weapon was available. However, the test results, and the effective use of the Hs-293A and Fritx-X on the Allies in the late summer of 1943, decided the issue.

A total of 15,000 AZONs was built through 1944. It was fielded in early 1944 in Europe, and was used operationally in attacks on targets in northern Italy. Since AZON, as its name implied, could be steered side to side but not up and down, it was suited to attacking long, narrow targets like bridges and viaducts. Results were unimpressive. First, AZON was difficult to use. Its effectiveness depended greatly on the training and skill of the operator in guiding a bright point of light to a target kilometers away.

Second, one bomber would drop multiple AZONs on a target, with the bombardier directing the first and hoping the others would follow. However, aerodynamic imbalances in individual bombs ended up dispersing the bomb pattern widely over the target. In fact, the dispersal was in general greater than it would be for unguided bombs. Unguided bombs rolled on the way down, reducing the effect of aerodynamic imbalances, while AZON was specifically designed not to roll, allowing imbalances to build up.

Weapons developers at first experimented with linking all the AZONs in a bombload together with a cable. This caused a whipsaw interaction among the bombs while they fell that made the bombs completely unguidable and generally snapped the cable. The engineers then tried a nylon rope, whose "rubber band" action made the interaction between the falling bombs even more interesting. They finally gave up and decided that only one AZON would be dropped by one bomber in each pass on a target, meaning only five AZONs could be used at a time, which was less than optimal for attacks on tough targets.

* AZON went into action against the Japanese in Burma in late 1944. Allied sea control was so tight that the Japanese could no longer send supplies to Burma by ship, and so supplies were sent by train from southern China instead. The northern Burmese terrain is very rugged, the rail routes required many bridges, and so these bridges very high priority targets for the USAAF. The Japanese understood this perfectly, and set up heavy anti-aircraft defenses to protect the bridges. That meant that USAAF heavy bombers had to bomb a target that was difficult to hit while dodging Japanese antiaircraft fire.

AZON seemed like a good solution, and a total of 459 of them were dropped, destroying 27 bridges. The fact that a bomber had to stay on course in the face of flak while its bombardier guided the AZON into a bridge was a dangerous nuisance, but the USAAF came up with a clever solution. Bombers were often escorted by P-38 Lightning fighters flying "top cover" over the bomber formation to provide protection against enemy fighters. The higher altitude of the fighters gave them some protection against flak, and the Japanese concentrated their fire on the bombers anyway, since they were the greater threat. A number of P-38s had been modified with clear "droop snoot" bomber noses to accommodate a bombardier, with these aircraft operating as "leads" for a flight of conventional P-38s carrying bombs and targeting for them; when the lead dropped its bombs, all the other Lightnings did as well. Some of the "droop snoot" P-38s were fitted with an AZON controller. A bomber would drop an AZON and then take evasive action, while the bombardier on board the droop-snoot P-38 would guide the AZON into the bridge.

* The attacks on Burmese bridges showed that radio-guided guided munitions had some potential, and advocates hoped that the next series of fully guided bombs would be even more effective. This series consisted of the fully guided "VB-3" (450 kilogram / 1,000 pound) and "VB-4" (900 kilogram / 2,000 pound) "RAZON (Range And Azimuth Only)" guided bombs, characterized by a double box tail. About 3,000 were built, but the weapon did not reach operational status during World War II.

Razon guided bomb

The USAAF experimented with other VB weapons that never got out of the test phase:

Roc glide bomb

The "VB-13", known as "TARZON" and later redesignated "ASM-A-1", was the only one of these later VB weapons to actually see action. It was a monster, a derivative of the British Tallboy deep-penetration bomb weighing 5.44 tonnes (12,000 pounds) and 6.4 meters (21 feet) long. It had a circular forward wing and a box tail, with four rudders on fins within the tail. It was, like the German glide bombs, radio-controlled and had a flare on its tail for optical tracking.

* Interest in such guided weapons declined in the years immediately after World War II. The electronics technology available was simply not reliable enough for combat use, and the experimental seeker systems suffered from low sensitivity and contrast. Despite these limitations, research continued at a low level, and in 1950, just before the beginning of the Korean War, the USAF began a RAZON field test program with the 19th Bombardment Group, which flew B-29 Superfortresses from Okinawa. However, various glitches prevented any RAZON drops until August 1950, when the war was in full burn.

The initial RAZON combat tests were a fiasco, due to reliability problems, poor crew training, and lack of proper equipment. The problems were finally under some degree of control by the end of September, and then the 9th flew a series of "bridge busting" raids against North Korea using RAZON. A single B-29 carried eight RAZONs. Many of the bombs were defective; of a total of 489 RAZONs dropped in Korea, only 331 worked. However, accuracy of the bombs that worked was very good, and with experience the bomber crews made better use of them. By the time RAZON drops ended in December 1950, they had destroyed 15 bridges.

The raids were helped by the fact that a 47-channel radio controller had been developed for RAZON, allowing up to 47 bombs to be guided at one time. However, the VB-3 was really too small to easily destroy a bridge. On the average, it took four direct hits from a 450 kilogram (1,000 pound) bomb to do the job.

The huge TARZON didn't have that problem, and TARZONs were sent to Okinawa in December 1950. They were so big that they could not be carried inside a B-29, having to be strapped to the belly of the aircraft. Records of the TARZON attacks are contradictory, but it appears that 30 were dropped, with six of them scoring direct hits on bridges and clearly destroying the targets. Unfortunately, there were other problems with the TARZON. Hauling around such a huge weapon was troublesome, and one B-29 carrying a TARZON disappeared over the ocean with its crew. The suspicion was that they had tried to dump the bomb at low altitude because of an emergency, and that it exploded on impact with the sea, taking out the aircraft along with it. TARZON missions were halted in August 1951.

Despite the problems, the overall results were encouraging. However, in the immediate post-Korean war timeframe, the US was desperately working on the nuclear option to keep ahead of the Soviets, and there were no resources available to work on tactical guided munitions. The technology generally went on the fade until the mid-1960s.

Surplus TARZONs were said to have been used as unguided munitions during the Vietnam War in Commando Vault operations to clear helicopter landing zones in the jungle. They were rolled out of the back of Lockheed C-130 transports and descended on parachutes. Apparently this practice led to the development of the BLU-82/B Big BLU bombs.



* The US Navy's (USN) experiments with glide weapons were even more obscure than those of the Army Air Force's, with one prominent exception.

The Navy experimented with "Bomb Gliders" of their own, which like the USAAF's weapons appear to have been unpowered drones; as well as an infrared-homing guided bomb named "Dove" that seems to have been similar to the USAAF's VB series. Details of these weapons are unclear.

The Navy also worked on a rocket-boosted glide weapon named the "Gargoyle", with the initial designation of "LBD-1", later changed to "KSD-1". The Gargoyle was conceptually similar to the Hs-293, and in fact may have been inspired by it. McDonnell was awarded a contract for five Gargoyle prototypes and 395 production missiles in September 1944. The Gargoyle carried a 450 kilogram (1,000 pound) armor-piercing bomb, built into a smoothly curved airframe with low-mounted rounded-tip wings and a vee tail. Length was 3 meters (9 feet 10 inches), wingspan was 2.6 meters (8 feet 6 inches), and total weight was 748 kilograms (1,650 pounds).

McDonnell Gargoyle

The Gargoyle was intended for launch by carrier-based strike aircraft, though apparently it was also considered for surface launch by rocket booster or catapult system. The missile had a solid rocket unit built into the tail to give it a launch boost, and was guided visually by an operator using a joystick connected to a radio link. As with the Hs-293, the Gargoyle had flares in its tail to allow the operator to track it.

Fourteen flight tests were performed from October 1944 through July 1945. The end of the war robbed the program of momentum, though test flights continued into 1947. The weapon was redesignated "RTV-2" in that year and then "RTV-N-2" in 1948, but by that time the effort was almost completely dead. There was some consideration after that of using the Gargoyle airframes as targets, but the program was formally axed in 1950.

* The prominent exception was the Naval Bureau of Ordnance's "Bat" antishipping weapon, which was fielded operationally, and was one of the most impressive guided weapons developed during World War II. Design work that led to the Bat began in 1941 and evolved through various forms.

The original concept was named "Dragon", given as the "Dryden Bomb" in some sources; one of the lead researchers on the project was Hugh L. Dryden of the National Bureau of Standards (NBS), who would later become one of the founding senior officials of the US National Aeronautics & Space Administration (NASA). It was defined as a radio-controlled glide bomb with a 900 kilogram (2,000 pound) warhead, with a plywood airframe designed by the NBS. A few were tested in 1942, but the Navy wasn't enthusiastic about the idea of the launch aircraft being forced to stick around up to weapon impact and quickly gave up on the concept. A TV-guided variant named "Robin" was then tested, but TV was simply not ready for combat at the time.

The research effort then moved on to the "Pelican" or "Special Weapons Ordinance Delivery (SWOD) Mark 7", which was intended for antisubmarine warfare. It carried a depth charge for attacks on surfaced U-boats, and was fitted with a "semi-active radar homing (SARH)" seeker that homed in on reflections from a radar beam provided by the launch aircraft. Use of a depth charge set to go off at shallow depth provided a higher "kill probability" against a submarine than a straight HE warhead.

Hitler's U-boats were decisively defeated in the spring of 1943 and the Pelican itself did not go into production. The Navy had built a fair stock of the Pelicans, however, and didn't want them to go to waste. Some were given sand-filled "warheads" and used as "Vulture" targets to train warship anti-aircraft gunners; others were fitted with a passive radar homing seeker and renamed "Moth", though they were never used operationally.

The only one of the SWOD series to reach production was the "SWOD Mark 9", the Bat. It was built around a 450 kilogram (1,000 pound) bomb and had a fully active radar seeker. Its NBS-designed airframe had a high wing and twin tailfins. The Bat was 3.63 meters (11 feet 11 inches) long, had a span of 3.05 meters (10 feet), and weighed 853 kilograms (1,880 pounds). Incidentally, some Pelicans were converted to a "Poor Man's Bat" configuration by the simple measure of adding a radar transmitter to complement the Pelican's SARH seeker. These weapons may have been used for trials, though some sources say there was a push to introduce them to combat on a fast-track basis; in any case, the Navy preferred to go on to the definitive Bat.

US Navy Bat

The Bat's guidance system was particularly sophisticated for the time. After being dropped, it glided toward the target on a preset course using a gyrostabilizer system to keep it on track. As it neared the target, the bomb locked on with its own radar system that guided it into the target. Since the radar seeker was conceptually similar to the "sonar" system used by a bat to prey on flying insects, the weapon was named after the bat. The Bat also included a self-destruct mechanism to keep it from falling into enemy hands, and obtained its electrical power from four small windmill generators.

The Bat was put into operation in May 1945, on Navy PB4Y-2 Privateer patrol bombers, maritime derivatives of the Consolidated B-24 Liberator. One Bat was carried under each wing. Privateers crews claimed many successes against Japanese shipping in the seas around Borneo, though some sources suggest they may have exaggerated the weapon's effectiveness. Bats with modified guidance systems were also used against ground targets in Burma and other Japanese-held areas; they simply homed in on the biggest target in their radar seeker.

The Navy tinkered with the Bat for a time after the war, successively renaming it "ASM-2" and then "ASM-N-2". However, its radar seeker was too easily spoofed and the weapon quickly faded into obscurity.



* In one of the more eccentric stories of World War II, the US military backed an investigation into weapons guided by trained pigeons. The investigation was conducted by the well-known behavioral psychologist Burrhus Frederic Skinner.

In early 1942, Skinner, then of the University of Minnesota, conducted preliminary studies on the concept of using trained animals as a guidance system. The studies were funded at a low level by General Mills, a major food producer. The US National Defense Research Committee (NDRC), which funded new technologies that might be useful for winning the war, was skeptical of the idea, but in mid-1943 awarded a $25,000 USD contract to General Mills to continue the work. The investigation was codenamed Project PIGEON (AKA ORCON for "Organic Control"), and Skinner hoped to be able to use pigeons to guide a weapon to within 6 meters (20 feet) of a target.

Three pigeons were each tucked into a jacket made of a sock and then put into a harness inside the guidance system, facing a screen. An image of the target was projected onto each of the three screens through a lens system in the nose of the weapon, with crosshairs defined by beams of light. Each pigeon was supposed to peck at its screen, which was wired to provide feedback to the missile's flight controls, to keep the crosshairs on target. The system accepted inputs from all three pigeons, but only acted if two or all three agreed. The pigeons were trained with slides of aerial photographs of the target, and if they kept the crosshairs on the target, they were rewarded by a grain deposited in a tray in front of them. Skinner later found that the pigeons were less easily disturbed under confusing circumstances if they were fed hemp (marijuana) seeds rather than grains.

Skinner hoped to fit the pigeon guidance system to a Pelican, but he never managed to overcome official skepticism. When he put on a demonstration in New Jersey of the pigeon guidance system for officials of the US Office of Scientific Research and Development (OSRD) he was bitterly frustrated to see they were amused instead of impressed.

Project PIGEON was abandoned. Skinner went home with 24 trained pigeons, which he kept in a dovecote in his garden. Whether the idea was practical or not, it appears that Skinner as a academic psychologist simply was not on the same wavelength as the industrial engineers and military officials he was trying to work with, and never managed to communicate with them effectively.