AN/APS-20

AN/APS-20. The AN/APS-20 was a powerful S band airborne search radar developed in the final year of World War II and became a cornerstone of post-war United States Navy and United States Air Force airborne early warning and maritime patrol operations. Its large, distinctive radome, housing an eight-foot antenna, was a common sight on a variety of carrier-based and land-based aircraft for nearly two decades. The system's long range and capability to detect surface vessels and low-flying aircraft made it a critical component of Cold War air defense and anti-submarine warfare networks.

Development and design

The development of the radar was driven by the United States Navy's urgent need for an effective airborne early warning system to counter the threat of kamikaze attacks against Task Force 38 and other naval formations in the Pacific Theater of Operations. Engineers at General Electric, building upon earlier radar technology like the AN/APS-6, created a system with a very high power output of approximately one megawatt and a large, mechanically scanned antenna to achieve superior detection range. The design operated in the S band, which offered a favorable balance between resolution and performance in various weather conditions. The massive antenna and its associated transmitter and receiver units were necessarily heavy, requiring installation on larger aircraft such as the TBM Avenger, which was used for initial testing and deployment before the war's end.

Operational history

The radar entered limited service aboard modified TBM-3W Avenger aircraft just prior to the end of World War II, seeing action in the final months of the conflict. Its true operational legacy was cemented during the Cold War, where it served as the primary search sensor for the United States Navy's first dedicated carrier-based Airborne Early Warning aircraft, including the AF-2W Guardian and the AD-3W/4W/5W Skyraider. The United States Air Force extensively utilized the system in the RC-121C/D and EC-121C/D Warning Star aircraft, which performed long-range surveillance missions for the Continental Air Defense Command and provided critical early warning during the Vietnam War. These aircraft, operating from bases like Wheelus Air Base and over international waters, played key roles in monitoring airspace and controlling intercepts for decades.

Variants

Several key variants of the radar were produced to suit different aircraft and missions. The initial production model was the **AN/APS-20A**, which was followed by the improved **AN/APS-20B** with enhanced reliability. The **AN/APS-20C** featured a modified display system for better operator interpretation. A significant advancement was the **AN/APS-20E**, which incorporated a Moving target indication capability to filter out ground clutter, greatly improving its ability to detect aircraft over land. This variant was vital for the United States Air Force EC-121 Warning Star operations. The **AN/APS-20F** was a further refinement, and the **AN/APS-20G** was developed with specific modifications for installation on the larger Lockheed WV-2 airframe. The basic technology also influenced later radar designs like the AN/APS-82 and AN/APS-95.

Specifications

The radar operated in the **S band** frequency range, with a peak power output of approximately **1 megawatt**. Its most distinctive physical feature was a parabolic reflector antenna **8 feet (2.4 meters)** in diameter, enclosed in a prominent fiberglass radome mounted under the aircraft's fuselage. The system provided a maximum detection range in excess of **100 miles** against large surface targets and could track multiple contacts. It required a dedicated radar operator and interfaced with various Identification friend or foe systems. The complete installation, including the antenna, waveguide, transmitter, and receiver units, was extremely heavy, often weighing several thousand pounds, which dictated its use on substantial aircraft platforms.

Operators

The primary operator of the radar was the United States Navy, which deployed it on carrier-based early warning aircraft throughout the 1950s. The United States Air Force operated it extensively on its EC-121 Warning Star fleet for continental defense and overseas surveillance. The Royal Navy evaluated and operated the radar, designating it **ASH**, aboard adapted aircraft like the Fairey Gannet AEW.3 and the Douglas Skyraider AEW.1 for fleet defense duties. The French Navy also utilized the system on a small number of modified TBM-3W aircraft for maritime patrol. The radar's service life extended into the late 1960s before being supplanted by more advanced systems like the AN/APS-96.

Category:American military radars Category:Airborne early warning and control Category:Cold War electronics of the United States