AN/APS-20

AN/APS-20
Hammersfan · CC BY-SA 3.0 · source
Name	AN/APS-20
Caption	AN/APS-20 airborne radar
Type	Airborne search radar
Introduced	1946
Manufacturer	Westinghouse Electric Corporation
Crew	Aircrew operator
Weight	~2,100 lb (950 kg)
Frequency	L-band
Power	1 MW (pulse)

AN/APS-20 The AN/APS-20 was a large airborne search radar developed for post-World War II maritime patrol and airborne early warning roles, introduced into service in 1946 and used by multiple naval and air forces through the Cold War. It influenced subsequent systems in airborne surveillance, antisubmarine warfare, and aircraft carrier operations, and was installed on platforms ranging from Lockheed P2V Neptune to Douglas AD Skyraider derivatives.

Development and Design

Development of the AN/APS-20 began in the late stages of World War II as part of efforts by United States Navy procurement to improve maritime reconnaissance and antisubmarine capabilities, with primary work carried out by Westinghouse Electric Corporation engineers influenced by wartime radar efforts such as Project Cadillac and lessons from the Battle of the Atlantic. Early design team interactions involved personnel from Radiation Laboratory alumni, exchanges with MIT and collaboration with contractors who had worked on the SCR-270 and ASV radar families. The program satisfied requirements set by Bureau of Aeronautics (BuAer) specifications and was accelerated during the transition from piston to early jet era aviation programs like Grumman TBM Avenger conversions and patrol initiatives led by Patrol Squadron 4 (VP-4).

Initial proposals evaluated antenna concepts used on ships such as the USS Intrepid (CV-11) and airborne installations tested on aircraft including Consolidated PBY Catalina and Boeing B-17 Flying Fortress prototypes. Westinghouse leveraged innovations from engineers formerly with General Electric and input from operators drawn from squadrons with combat experience in the Pacific Theater and European Theater of Operations (WWII). The design balanced considerations from Naval Air Systems Command planners and influenced early NATO maritime air doctrine discussions involving delegations from Royal Navy and Royal Canadian Navy observers.

Technical Description

The AN/APS-20 operated in the L-band microwave spectrum and employed a large parabolic antenna housed in a ventral radome; its transmitter delivered high peak power pulses enabling long-range surface-search and low-flying aircraft detection capabilities similar in purpose to systems used on Lockheed SR-71 predecessors and contemporaries such as AN/APS-4. Key subsystems were derived from technologies advanced by Bell Labs and components manufactured by suppliers with pedigrees tracing to Raytheon and Hughes Aircraft Company. The radar featured pulse-Doppler elements influenced by research at Harvard University and signal-processing concepts explored at Lincoln Laboratory, while operators monitored Plan Position Indicator scopes and Tactical displays akin to those standardized in Naval Tactical Data System experiments.

Electromechanical assemblies reflected practices from Curtiss-Wright and AlliedSignal manufacturing, with ruggedization requirements informed by carrier operations aboard ships like USS Essex (CV-9). Power systems and cooling incorporated designs comparable to airborne installations on Lockheed P-2 Neptune and maintenance procedures referenced documentation standards from National Bureau of Standards. The antenna rotation, beamforming, and stabilization mechanisms borrowed from naval gunnery servo work seen on Bofors 40 mm mount servo trials and cooperative studies with Pratt & Whitney propulsion engineering groups to assess vibration environments.

Operational History

AN/APS-20 installations entered service in the immediate postwar period with United States Navy patrol squadrons and were deployed aboard maritime patrol aircraft including Lockheed P2V Neptune, Douglas AD Skyraider variants, and specialized conversions of Consolidated PB4Y-2 Privateer. The radar supported Cold War antisubmarine warfare missions against Soviet Navy submarine deployments, participated in surveillance patrols during crises such as the Korean War and early Vietnam War maritime monitoring, and aided carrier strike group operations alongside Carrier Air Group assets. Crews from units like VP-6 and VS-24 used the AN/APS-20 for search and vectoring of surface contacts, cooperating with ships such as USS Midway (CV-41) and USS Franklin D. Roosevelt (CVB-42) in coordinated maritime searches.

Allied operators included Royal Canadian Air Force squadrons operating Avro Lancaster maritime variants and Royal Navy units that fitted the system to aircraft like the Fairey Gannet in trials. The radar played roles in major Cold War incidents involving naval shadowing, early warning sorties tied to events like the Suez Crisis and NATO maritime exercises coordinated with Standing Naval Force Atlantic formations. Field feedback from operational use drove tactics later codified in procedures at Naval War College seminars and informed signals intelligence cooperation with agencies such as National Security Agency liaison teams.

Variants and Upgrades

Several variants and upgrades adapted the core AN/APS-20 electronics, packaging, and installation interfaces for different platforms and missions. Avionics modernization efforts paralleled programs at Grumman Aircraft Engineering Corporation and retrofit initiatives by Lockheed Martin predecessors, creating versions with improved receivers, clutter rejection, and IFF integration compatible with Identification Friend or Foe transponders. Platform-specific adaptations included lighter-weight installations for carrier-borne aircraft influenced by Douglas Aircraft Company structural constraints and stabilized radome assemblies developed with input from Goodyear Aerospace engineers.

Later lifecycle upgrades incorporated more advanced signal processing modules inspired by developments at Massachusetts Institute of Technology Lincoln Laboratory and digital component transitions similar to those used in the AN/APS-95 family. Field modification kits provided by Westinghouse and subcontractors from Sperry Corporation addressed maintainability and parts commonality, aligning with logistics philosophies taught at Defense Logistics Agency workshops.

Operators and Deployments

Primary operators included the United States Navy and United States Air Force maritime reconnaissance units, with international users such as the Royal Canadian Air Force, Royal Navy, French Navy, Royal Australian Air Force, and navies of Italy, Netherlands, and Japan. Aircraft types fitted with the radar encompassed Lockheed P2V Neptune, Consolidated PB4Y-2 Privateer, Avro Shackleton trials, and ad hoc installations on transports and early electronic warfare platforms. Deployments spanned patrol sectors in the North Atlantic Treaty Organization maritime regions, Pacific surveillance zones including the Western Pacific, and Mediterranean patrols tied to Six-Day War era tensions and Cold War fleet shadowing episodes.

Legacy and Impact

The AN/APS-20 influenced the evolution of airborne maritime surveillance systems and contributed to doctrines developed at institutions like Naval Postgraduate School and United States Naval Institute publications. Technological advances pioneered in its design informed successors such as airborne radars used on Lockheed P-3 Orion and carrier airborne early warning platforms that trace lineage to innovations evaluated by Project Mercury era avionics researchers. The system’s operational history is discussed in works by historians associated with Smithsonian Institution collections and in technical retrospectives produced by former Westinghouse engineers archived at Institute of Electrical and Electronics Engineers repositories. Its legacy persists in modern maritime patrol sensor integration taught at Fleet Anti-Submarine Warfare Training Center and referenced in analyses of Cold War maritime reconnaissance strategies.

Category:Airborne radars