BG and GB SERIES

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he 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:

The “BG (bomb glider)” series.
The “GB (glider bomb)” series.
The “VB (vertical bomb)” series.
There is little information available 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 questionable, 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 were 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:

The “GB-5” was fitted with a crude electro-optic (EO) seeker that homed in on high-contrast targets.

The “GB-6” was fitted with an infrared heat-seeker.

The “GB-7” was fitted with a passive radar homing seeker.

The “GB-8” was fitted with a radio control scheme. The result was not so different from that used by the Hs-293, with the operator tracking it by watching red and white flares attached to the airframe; it may have had a solid-fuel boost rocket.

The “GB-11” was a GB-1 with the bomb replaced by a chemical-agent dispersal tank. It leveled off at low altitude to disperse the chemical agent behind it.

The “GB-12”, originally “GB-5C”, was a GB-5 with a different EO seeker.

The “GB-13”, originally “GB-5D”, was a GB-5 with a seeker that homed in on target marking flares.

The “GB-14”, original “GB-7B”, was a GB-7 with an active radar seeker. It was generally redesigned and had a strong resemblance to the US Navy Bat, discussed later.
These munitions never got out of the test stage and were cancelled 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, and was 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.

• 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:

The “GB-9” was modified to dive to build up speed until a radar altimeter indicated it had passed a preset altitude. It would then level out to be radio-guided into the target at a low angle. It was designed to destroy targets that were tough to attack from above, such as submarine pens.

The “GB-15” was apparently a GB-4 follow-on, with radar or TV guidance, but details are unclear.
As with the GB-1 variants, none of these weapons got out of the test stage, and were all cancelled 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.