VB-6 Felix

The VB-6 Felix was an experimental precision-guided munition developed by the United States Army Air Forces during World War II, consisting of a modified 1,000-pound general-purpose bomb equipped with an infrared heat-seeking nose section and steerable tail control surfaces for autonomous homing on targets emitting elevated thermal radiation, such as blast furnaces or sun-heated industrial structures.^[1]^[2] Developed under the oversight of the Army Air Technical Service Command (ATSC), the VB-6 incorporated a 84-pound nose assembly with an octagonal shroud and bolometer-based infrared sensor that adjusted control surfaces to steer the weapon toward heat sources contrasting with cooler surroundings, while the 143-pound tail unit provided gyro-stabilized ailerons and rudders for stability during high-angle release trajectories.^[3]^[2]^[4] Overall, the weapon measured 91.2 inches in length and 18.6 inches in diameter, with a total weight of 1,202 pounds, including its AN-M65 warhead armed by a T85 nose fuze and M167 tail fuze, and it was suspended from standard bomb lugs for release via the Norden bombsight in clear weather conditions.^[2] Intended primarily for precision strikes against heat-radiating industrial targets to minimize collateral damage, the VB-6 demonstrated promising test results in 1945 but saw no production or combat deployment before the war's end led to program cancellation.^[1]^[3] As one of the early efforts in guided munitions technology, the VB-6 shared conceptual similarities with contemporaneous projects like the U.S. Navy's ASM-N-4 Dove, influencing post-war advancements in infrared-guided weaponry, though surviving examples remain in storage at institutions such as the National Museum of the United States Air Force.^[3]^[5]

Development

Origins and Requirements

The development of the VB-6 Felix emerged from the strategic imperatives of World War II, where the United States required advanced precision-guided munitions to enhance the accuracy of Allied bombing campaigns against high-value, heat-emitting targets. These included industrial facilities such as German blast furnaces and coke ovens, as well as Japanese shipyards, which radiated significant thermal signatures but proved challenging to strike effectively with conventional unguided bombs due to factors like high-altitude releases and adverse weather conditions.^[1]^[6] Oversight for the VB-6 project was provided by the National Defense Research Committee (NDRC) Division 5 and the Army Air Technical Service Command (ATSC), which initiated the effort in 1944 through contracts including NDC-rc-180 with the Massachusetts Institute of Technology (MIT) and NDC-rc-183 with Gulf Research. The core requirements called for a 1,000-pound-class bomb equipped for autonomous homing on thermal signatures, enabling it to detect and track targets independently after release.^[6] The project was designated "Felix" by NDRC Division 5, reflecting its heat-seeking technology.^[6] Early specifications envisioned the VB-6 as a free-fall glide bomb deployable from medium-altitude bombers at 15,000 to 20,000 feet, with control surfaces activating around 10,000 feet to guide it toward thermal sources over distances of 3 to 5 miles for isolated targets. Its dual roles emphasized anti-ship strikes against vessels like 6,500-ton class freighters and industrial sabotage against heat-radiating infrastructure, positioning it as a key component in the U.S. VB-series of guided bombs without relying on radio commands for terminal guidance.^[6]^[3]

Research and Production

The research and development of the VB-6 Felix was initiated in early 1944 under the auspices of the National Defense Research Committee (NDRC) Division 5, with primary oversight by the U.S. Army Air Forces Materiel Command, the Army Air Technical Service Command (ATSC), and the Air Proving Ground Command (APGC).^[6] NDRC Section 5.2 coordinated contracts, including NDC-rc-180 with the Massachusetts Institute of Technology (MIT) and NDC-rc-183 with Gulf Research and Development Company, focusing on adapting infrared detection technologies derived from radar and photoelectric experiments for heat-seeking guidance.^[6] These efforts built on bolometer-based infrared seekers, utilizing a nickel strip bolometer paired with a rotating parabolic mirror to detect thermal emissions in a 200-foot diameter field, sensitive to approximately 1 erg/cm²/sec.^[4]^[6] The project emphasized integration of the seeker into a standard 1,000-pound bomb equipped with octagonal control surfaces and tail-mounted actuators for stability during high-angle drops from altitudes of 15,000 to 20,000 feet, with seeker activation around 10,000 feet.^[6] Key challenges included overcoming spurious signals from atmospheric heat gradients that limited effective homing to targets within a 1,500-foot radius.^[6] Electrical and mechanical defects in early prototypes were identified and corrected iteratively, drawing on empirical adaptations of pre-war photoelectric research to enhance seeker reliability without advanced semiconductor knowledge.^[4] By mid-1945, preproduction models were completed under Army supervision at contractor facilities, with a small number of units manufactured to support trials, though a proposed program for 1,000 units was curtailed by the war's end.^[6] Production costs were tied to resource allocations from NDRC and Army Air Forces priorities, emphasizing rapid prototyping over mass scaling, and the effort concluded with the end of World War II in 1945, without full production or combat use, though it represented an early U.S. effort in infrared-guided bombs with limited preproduction units.^[4]

Design

Airframe and Warhead

The VB-6 Felix was constructed around the standard 1,000-pound general-purpose (GP) bomb body, designated AN-M65, with an added nose section and tail assembly to incorporate guidance capabilities.^[2] The overall length measured 91.2 inches (231.6 cm), with a diameter of 18.6 inches (47.2 cm), and the total mass reached 1,202 pounds (545 kg).^[2] The airframe featured an octagonal control shroud at the tail, equipped with movable range and azimuth control surfaces as well as gyro-stabilized ailerons for steering during glide.^[2] The warhead consisted of the AN-M65 GP bomb body filled with approximately 530 pounds (240 kg) of amatol explosive, a mixture of ammonium nitrate and TNT designed to provide both penetration and blast effects suitable for hardened industrial targets.^[7]^[2] This filler was housed in a steel casing with an ogival nose and tapered aft section, optimized for high-explosive delivery in general-purpose roles.^[7] The nose-mounted seeker housing, weighing 84 pounds (38 kg), integrated the heat-seeking components without altering the core bomb structure, while the 143-pound (65 kg) tail assembly provided the necessary aerodynamic controls.^[2] The VB-6 was designed for aerial release from bombers such as the B-17 Flying Fortress at altitudes of 15,000 to 20,000 feet (4,600 to 6,100 meters) to achieve effective high-angle glide trajectories.^[1]^[6]

Guidance and Control Systems

The VB-6 Felix employed an infrared seeker mounted in the nose, utilizing a nickel strip bolometer positioned at the focal point of a parabolic mirror with a 1-inch focal length and 2-3/8-inch aperture.^[8] This bolometer detected thermal radiation from heat-emitting targets, such as blast furnaces or industrial installations, with a sensitivity of approximately 1 erg/cm²/sec during flight, enabling homing on sources significantly hotter than the ambient environment.^[8] The seeker scanned a 20° field of view by rotating the mirror 5° off its optical axis, dividing the field into four quadrants via electronic switches and relays to determine the target's position relative to the bomb's centerline.^[8] Control was achieved through four movable fins integrated into the octagonal tail shroud, actuated by servo motors in the tail assembly that responded to signals from the seeker.^[3]^[8] A gyro-stabilized frame coupled the seeker's orientation to the fins, providing corrections in pitch, yaw, and roll; rudders handled yaw, while elevators managed pitch, with the system connected via a flexible cable from the nose electronics to the tail actuators.^[8] These mechanisms operated during the guided glide phase, typically lasting 20-30 seconds after release from altitudes of 15,000-20,000 feet (4,600-6,100 meters), with control initiating via an automatic timing switch after about 20 seconds of free fall to reach approximately 10,000 feet.^[8]^[1] The guidance logic followed a proportional navigation approach, where the seeker continuously tracked thermal contrast and steered the bomb toward the detected heat source without requiring pilot intervention post-release.^[8] Upon detecting a target in one quadrant, relays activated the corresponding fin deflections to oscillate the bomb toward the source, progressively aligning it with the line of sight until impact; this autonomous homing was effective within a control radius of about 1,500 feet.^[8] The system's power was supplied by a small battery pack within the control head, energizing the electronics, relays, and servo motors upon arming, which occurred through the timer or an altimeter-based sequence to ensure safe release.^[8]

Testing and Performance

Development Trials

The development trials of the VB-6 Felix included seeker evaluations and flight tests to verify the infrared guidance system. The project was overseen by the National Defense Research Committee (NDRC) Section 5.2 under contracts with MIT and Gulf Research.^[6] The heat seeker featured a nickel strip bolometer at the focal point of a rotating parabolic mirror with a 20° field of view and sensitivity requiring ~1 erg/cm²/sec. Airplane-mounted tests evaluated homing capability, achieving ranges of 3-4 miles against ships, 3-5 miles on isolated land targets like steel mills, and up to 15 miles on industrial areas in cities under clear conditions.^[6] Flight testing in 1945 utilized B-17 bombers for drops from 15,000-20,000 feet, with control activating at around 10,000 feet. A total of 12 experimental drops were conducted using preproduction models, demonstrating a control radius of ~1,500 feet. Performance was satisfactory despite some electrical and mechanical failures.^[6]^[3]

Accuracy and Limitations

The VB-6 Felix achieved a mean circular error probable (CEP) of 85 feet from the 12 experimental drops, with 11 of 12 bombs landing within a 200-foot radius of the target under ideal conditions. These results were obtained in clear atmospheric environments against differential thermal signatures. Efficacy depended on target contrast and high-altitude release parameters for glide path stability.^[6] Compared to unguided ordnance, the VB-6 offered significantly improved precision, but its free-fall glide dynamics and early infrared technology imposed limitations. The effective homing range was approximately 3-5 miles based on seeker tests. The system was vulnerable to spurious signals from horizon heat gradients, restricting use to release angles of 80° or greater, with ongoing work on improved seekers. No propulsion limited standoff capability, and the design lacked jamming resistance or multi-spectral sensing. While promising, these factors and the war's end prevented deployment.^[6]^[3]

Variants and Derivatives

VB-6 Configuration

The VB-6 Felix served as the standard configuration of the guided bomb developed under the U.S. Army Air Forces' designation, optimized for delivery from land-based heavy bombers such as the B-29 Superfortress. This setup featured a 1,000-pound general-purpose bomb body fitted with movable control surfaces for gliding flight and an infrared heat-seeking guidance system in the nose, enabling homing on heat-emitting targets like blast furnaces or industrial facilities.^[1]^[9] The design emphasized high-altitude, high-angle drops to support precision strikes in strategic bombing campaigns.^[9] Intended for integration into B-29 raids targeting Japanese industrial infrastructure in the Pacific theater during late 1945, the VB-6's deployment was planned to enhance accuracy against heat-radiating sites such as steel mills and factories.^[9] The VB-6 never entered combat service, with test units primarily expended during developmental trials or reserved for evaluation rather than operational deployment.^[1] Post-war, surplus VB-6 units were demilitarized, stored, or repurposed for continued research and testing by the 1st Experimental Guided Missiles Group through 1948, after which the project was fully terminated amid the shift to nuclear and missile priorities.^[1] One exemplar remains in storage at the National Museum of the U.S. Air Force as a historical artifact.^[1]

ASM-N-4 Dove

The ASM-N-4 Dove originated as a U.S. Navy adaptation of the Army Air Forces' VB-6 Felix guided bomb, initially developed by the Polaroid Corporation with Navy funding starting in April 1944, and the project designated Dove.^[10]^[11] In July 1946, following the end of World War II, the Navy transferred the Dove technology to Eastman Kodak for further development as an air-to-surface guided weapon.^[11] The designation was formalized as ASM-N-4 in early 1948, reflecting its classification as a Navy air-to-surface missile.^[10] The Dove retained the infrared seeker inherited from the VB-6 Felix for heat-homing on targets but was modified for naval applications, including improved targeting of ships and industrial sites with distinct infrared signatures.^[10] It utilized the AN-M65 1,000-pound general-purpose bomb as its base airframe, fitted with tail control fins and a nose-mounted infrared sensor, allowing drops from altitudes up to 30,000 feet (9,100 meters).^[10] The design emphasized precision guidance over extended range, though no propulsion system was incorporated.^[10] In 1949, the Navy awarded Eastman Kodak a contract to produce 20 XASM-N-4 prototypes for testing.^[10] Trials, overseen by the Bureau of Ordnance, involved evaluating the missile's infrared homing and control systems against simulated targets, with evaluations concluding in October 1952.^[10] Despite successful prototype construction and testing, the program did not advance to full production.^[11] The Dove project was ultimately cancelled in 1955 amid post-war budget constraints and the rapid evolution of more advanced guided weapons, such as the ASM-N-7 Bullpup, which entered service shortly thereafter.^[12]