AN/APQ-112

AN/APQ-112. The AN/APQ-112 was an X-band airborne fire control radar system developed by General Electric for the United States Air Force. It was a key component of the AN/ASG-26 Thunderstick bombing system integrated into the Republic F-105 Thunderchief, a principal aircraft during the Vietnam War. The system provided critical ground-mapping and ranging capabilities for delivering Mk 84 and M117 general-purpose bombs, as well as AGM-12 Bullpup air-to-surface missiles, in all-weather conditions.

Development and design

The development of the radar was driven by the United States Air Force's requirement for a precision bombing and navigation system for its new generation of tactical fighter-bombers in the late 1950s. Engineers at General Electric designed the system to be compatible with the complex AN/ASG-26 Thunderstick analog computer, which processed data for weapon release. The design utilized a planar array antenna housed in the nose radome of the Republic F-105 Thunderchief, providing a narrow beam for improved resolution. Key design challenges involved achieving sufficient reliability and maintenance access within the cramped confines of the Republic Aviation aircraft, leading to a unit that was often difficult for ground crews from the Strategic Air Command and Tactical Air Command to service in field conditions.

Operational history

The system entered service with the United States Air Force in the early 1960s, primarily equipping the Republic F-105 Thunderchiefs of units like the 355th Tactical Fighter Wing and the 388th Tactical Fighter Wing. It saw extensive combat use during the Vietnam War, particularly in operations like Operation Rolling Thunder and Operation Linebacker II against targets in North Vietnam. Pilots relied on its ground-mapping mode for navigation and its ranging function for dive-toss bomb deliveries against bridges, rail yards, and surface-to-air missile sites. However, its performance was often degraded by heavy electronic countermeasures employed by the North Vietnamese Air Defense Network, and its complexity led to significant maintenance challenges for squadrons deployed to bases like Takhli Royal Thai Air Force Base and Korat Royal Thai Air Force Base.

Technical specifications

The radar operated in the X-band frequency range, providing a typical detection range against large ground targets. It featured several operational modes, including a high-resolution ground-mapping mode for navigation and a precise ranging mode for weapon delivery calculations. The antenna was a planar array type, mechanically scanned, and interfaced directly with the AN/ASG-26 Thunderstick bombing computer. The system required significant electrical power from the Republic F-105 Thunderchief's generators and was cooled by the aircraft's environmental control system. Its performance was notably affected by weather conditions and terrain, with limitations in very heavy rain or over perfectly flat terrain.

Variants

The primary variant was the baseline model installed in most Republic F-105 Thunderchief D and F models. An improved version, sometimes unofficially referenced in conjunction with updates to the overall AN/ASG-26 Thunderstick system, incorporated minor reliability modifications based on combat experience from the Vietnam War. No fundamentally different model with a distinct designation was widely produced, as the system was ultimately supplanted by newer technologies like the AN/AVQ-23 Pave Spike laser designator pod and more advanced radar systems in aircraft such as the General Dynamics F-111 Aardvark.

Operators

The sole operator was the United States Air Force. The system was used exclusively by units flying the Republic F-105 Thunderchief, including wings under both the Tactical Air Command and, for a period, the Strategic Air Command. Key operating units during the Vietnam War included the aforementioned 355th Tactical Fighter Wing, 388th Tactical Fighter Wing, and the 23rd Tactical Fighter Wing. With the retirement of the Republic F-105 Thunderchief from frontline service in the early 1980s, the system was completely phased out of inventory.

Category:Aviation radars Category:United States Air Force avionics Category:Military electronics of the United States