Guided Bombs in Korea


The VB-3 Razon (for range and azimuth) was a standard 1,000-pound general purpose bomb fitted with flight control surfaces. Development of the Razon began in 1942, but it did not see use during World War II.


The ASM-A-1 Tarzon, also known as VB-13, was a guided bomb developed by the United States Army Air Forces during the late 1940s. Mating the guidance system of the earlier Razon radio-controlled weapon with a British Tallboy 12,000-pound (5,400 kg) bomb, the ASM-A-1 saw brief operational service in the Korean War before being withdrawn from service in 1951.

As with aircraft design, guided weapons development did not cease in the aftermath of World War II. Allied and German progress in the latter stages of the war appeared so promising that a number of related projects were contracted by the U. S. military throughout the late 1940s. Not surprisingly, much of the emphasis within the munitions community in the early postwar period remained on further development and testing of atomic weapons. However, following the Operation Sandstone atomic bomb tests of early 1948, Air Proving Ground Command reorganized several of its units returning from the Marshall Islands to create a 750-man group dedicated to the acquisition of guided weapons. Based at Eglin Air Force Base, in the Florida panhandle, the 1st Experimental Guided Missiles Group was specifically charged to develop tactics and techniques for guided missile operations. Although the term “guided missile” conjured up images of exotic weaponry that captured the imagination of neighbors in nearby Fort Walton Beach, as used in the postwar period it designated the limited mix of existing guided weapons, all of which had pre-1945 antecedents.

By December 1948 the Group was conducting proving demonstrations on four distinct guided weapons, only one of which was a self-propelled missile. However, the one thing that all four did have in common was the implementation of radio control for guidance. The most “missile-like” weapon under test, the JB-2, was simply an American adaptation of the German V-1, or “Buzz-Bomb.” Powered by a pulse-jet engine, this short-range, high-explosive missile was modified to allow launch from a parent aircraft and adapted to guidance either by preset data or remote radio control while in right. Capable of a fifty-mile range at speeds up to 440 miles per hour, the fact that the JB-2 was never fielded was more a function of its inaccuracy, which was in the half-mile range, than the mere result of budget constraints. Another Guided Missiles Group project that likewise never saw production was Project Banshee. Hoping to prove that “a pin-point target can be precision-bombed by remote control, at a very long range from an operating base,” Banshee underwent operational testing beginning in February 1949. Using equipment designed and fabricated by General Electric and RCA, airmen were able to fry a B-29 aircraft 2,000 miles and drop a bomb on a target by remote control, using two airborne navigation stations. Despite achieving “excellent” results on several test rights, it became clear that the electronic equipment still suffered from technical difficulties. Beyond this, even at its best Banshee could hope to achieve an accuracy no better than a manned B-29 bomber.

Not every early postwar test project ended in obscurity-in fact, two survived to see not only quantity production but also actual combat in Korea. Classified as air-to-surface missiles, these two weapons were a continuation of the wartime high-angle bomb project, and bore the designation “VB” for vertical bomb. Similar to the VB-1 Azon, discussed in the previously, the VB-3 Razon bomb consisted of a free-falling M-65 1,000-pound general-purpose bomb, fitted with a special tail section for guidance. Like Azon, the tail fins contained the equipment necessary to receive transmitted radio signals from the aircraft and apply the appropriate control surface movements. However, in place of cruciform fins, the Razon tail employed a pair of in-line octagonal shrouds-the rearmost containing the elevators and rudders that allowed the bomb to be controlled in both azimuth and range-mounted on struts containing roll stabilization surfaces. In practice, Razon was controlled by a bombardier using a method reminiscent of earlier Azon and Fritz-X deployment, namely by means of a rare attached to the bomb’s tail and superimposed upon the target through the optics of a bombsight.

In order to remedy the parallax problem that had plagued wartime engineers’ attempts at range guidance, the standard M-series Norden bombsight was modified with a clever crab and jag attachment. The “crab” portion of this device consisted of a mirror placed between the target mirror and the telescopic lens system of the bombsight. This mirror not only projected an image of the rare onto the target mirror but also calculated the correct time of fall when the trail angle set into the sight was aligned exactly with the angle of the “crab” mirror setting. In principle, this allowed the bombardier to simply superimpose the rare image on the target throughout bomb descent using a radio control joystick. However, because any movement of the bomb’s control surfaces during the drop caused a variation in the time of fall, affecting range, the “jag” attachment was introduced to compensate for this effect by changing the rate set into the bombsight each time course corrections were made. In theory, by keeping the images of the rare and target in perfect collimation via radio control throughout the bomb’s descent, a bombardier could score a direct hit with Razon virtually every drop. In actuality, testing still showed Razon to be far more accurate in azimuth than range. For example, of the eight bombs tested in August 1948, fully three out of four had an azimuth error of zero, while the average range error was almost 200 feet. Only one of the eight scored a direct hit. Still, Razon bombing showed enough promise in early testing that approximately five hundred tail assemblies were produced by Union Switch and Signal Company and stockpiled, allowing their use in the early months of the Korean War.

Although development and testing of a second vertical bomb, the VB-13 Tarzon, trailed Razon, it too had its roots in the World War II high-angle dirigible bomb project. Realizing that some of Azon’s deficiencies in accuracy could be negated through increased firepower-in this case, bomb tonnage- Gulf Research and Development Corporation received Army authorization in February 1945 to investigate the aerodynamic aspects of the problem of controlling larger bombs. Simple scaling up of Razon proved unsatisfactory, since the derecting forces on a given bomb increase with the square of the diameter, while the mass to be controlled increases as the cube of the diameter. A larger bomb thus required disproportionately larger control surfaces- which, in turn, magnified the problem of range error due to variation in time of fall-and limited in number and placement its carriage by existing bombers. Several preliminary models were built in mid-1945 but failed to reach combat, and by 1947 the NDRC was still of the opinion that “future developments in this field will require considerable fundamental research.”

Ironically, at the time this NDRC report was issued, Bell Aircraft Corporation had already developed a working solution involving a bomb an order of magnitude larger than Azon and Razon. Once again following technological precedent, Bell designed only a bomb tail guidance assembly to be mated to an existing bomb. In order to gain the full advantages of increased yield, however, the warhead selected for this project was the British “Tallboy,” a 12,000-pound bomb in use by Bomber Command by 1944, and procured by the Air Force as the general-purpose M-112 bomb following the war. The name of the resulting guided weapon, Tarzon, was arrived at as a clever-sounding pseudo-acronym combining Tallboy, range, and azimuth only. In order to produce sufficient force to steer Tarzon without introducing giant fins that would exceed a standard bomb bay, Bell attached a lift ring to the warhead around the bomb’s approximate center of gravity. The effect of this ring shroud was to greatly amplify directional changes introduced by the tail surfaces, much like the wings of an airplane. However, this ingenious solution to heavy bomb guidance was not itself without antecedent. In order to adapt its NDRC-sponsored Roc radar-guided bomb to naval aircraft in 1944, Douglas Aircraft Company had replaced large crossed wings with a ring shroud, greatly reducing its cross-sectional area. Even so, Tarzon measured twenty-one feet in length, four and one-half feet in diameter, and with a gross weight of 13,000 pounds, could be dropped only by a specially modified B-29 Superfortress with cutouts in the bomb bay doors, and was limited to a single bomb per aircraft sortie.

In virtually every other respect, Tarzon was an enlarged version of Razon. For example, its tail section consisted of an octagonal shroud containing pitch and yaw control surfaces, connecting struts with roll stabilization surfaces, a rare cone, and a center section containing the radio receiver, gyroscope, batteries, and servomotors. Guidance equipment aboard the launching aircraft similarly consisted of a radio transmitter controlled by a two-axis control stick, and a Norden M-series bombsight modified with crab and jag attachments. Although development of Tarzon lagged Razon by several years, testing of the two bombs was performed concurrently in 1948-49 by the 1st Experimental Guided Missiles Group. However, because of its greater size and cost, and retarded development, far fewer Tarzon bombs were dropped on Eglin test ranges during this period. For example, during the month of August 1948, as four Razon drops per week were contributing to improved tactics, training, and accuracy, a single Tarzon was expended to determine the effect of applying maximum up control using a recently modified tail assembly. By mid-1949, Razon had been upgraded with “the newest modification of radio control equipment” and underwent extensive testing under a variety of conditions, including night rights. During this same period, Far East Air Forces sent two airmen from Japan to Eglin for “training in the tactical application of VB-type bombs,” where they participated in a variety of missions and dropped sixteen Razons before returning to their unit. Meanwhile, Tarzon testing under cold weather conditions produced results that “were at best only fair, due to rare failure.”

Notwithstanding the steady introduction of new technology throughout the late 1940s, the early fighting in Korea closely resembled that of World War II-familiar faces and weapons engaged in a familiar war-winning strategy. However, the exploitation of existing jet fighter technology, which rapidly translated into American air superiority, created a combat environment conducive to the introduction of precision bombardment at a time when the ground situation desperately called for it. The radio-controlled vertical bombs just described were not the only postwar attempts at precision. In 1949 the 1st Experimental Guided Missiles Group took on seven additional test projects, including the VB-6 Felix, a heat-seeking bomb designed to steer itself toward the target producing the highest temperature emanation within the twenty-degree scope of its forward sensor. Felix was envisioned as a decisive tactical weapon, but initial tests were disappointing. Although the decision to return the bomb to the research and development phase was based primarily on insufficient reaction speed of its control surfaces, the final test report also noted “lack of a suitable target during this time would also negate any efforts to test it, even if a theoretically workable model was available.” Thus, as America went back to war in 1950, its best prospects for precision guidance bore a remarkable resemblance to the radiocontrolled weapons used during World War II.

Once war broke out, it did not take long for bombing accuracy to surface as a deficient capability. Specifically in the realm of strategic bombardment, despite the use of sophisticated, computer-assisted bombing systems such as the Air Force’s K-series, CEPs remained in the 500-foot range, far from optimal given North Korea’s rugged terrain and segregated targets. Not surprisingly, as the only guided weapon in quantity production prior to 1950, Razon emerged early in the conflict as a promising alternative to gravity bombs. As previously noted, preparations for the implementation of Razon by Far East Air Forces bomber crews anticipated the Korean conflict. As early as 1949, Air Proving Ground had trained three officers and six enlisted men of the 19th Bombardment Group for Razon work and in early 1950 began delivering specially equipped aircraft and a supply of Razon tail assemblies to this same group, which was based on the Japanese island of Okinawa. Clearly, the intent was to establish a training cadre that would instruct additional aircrews of this group to use Razon. However, shortly after the outbreak of war in Korea, it became apparent that neither the personnel nor the equipment was being utilized, and Far East Air Forces headquarters turned to the Air Proving Ground for additional assistance.

Because of the resulting delay in assembling the necessary equipment and personnel, the 19th Bombardment Group did not fry its first Razon combat mission over Korea until August 23, 1950. Even then, the first several missions produced unsatisfactory results because of frequent bomb malfunctions, some caused by damage from the bombs’ long storage and poor packaging, and some by the relative inexperience of the group’s operators and maintainers. Moreover, even though missile reliability quickly rose to 96 percent, from the outset Razon remained far more accurate in azimuth than in range, making it a weapon best suited for use against long, narrow targets. Like its Azon predecessor, Razon was used almost exclusively against bridges in Korea, with defensible results-during the last four months of 1950, fifteen Korean bridges were destroyed using Razon bombs. However, to put these results into perspective, a total of 489 Razons were dropped during this period, of which 331 were controllable. Razon was far from attaining the long-sought single-bomb destruction capability, and yet it had its supporters. The low percentage of targets destroyed was partially attributable to the fact that limited equipment and crews forced training to be combined with combat missions. As an example, one bombardier destroyed two bridges with his first two bombs, but was then instructed to drop the remaining six for practice. In every case where a bridge was destroyed by Razon, additional bombs were dropped on the same target for practice. Although clearly not unbiased, the onsite Razon project officer estimated that “any bridge can be successfully severed or destroyed with a maximum of four Razon missiles.

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