Douglas B-18B 37-530 with MAD tail antenna and SCR-517A radar
In early 1942, the U.S. military faced significant challenges in converting the SCR-520 radar systems, initially designed for short-range air interception (AI), into the SCR-517A configuration, which was meant for long-range air-to-surface (ASY) operations. This conversion was essential to enhance the capability of aircraft in anti-submarine warfare (ASW) during a critical period when U-boats were wreaking havoc on Allied shipping.
Conversion Challenges
- Technical Issues:
- The primary difficulties in converting the SCR-520 to the SCR-517A lay in adjusting the speed of the antenna’s rotation and the angle of the reflector, essential for transitioning from AI to ASY functionality. These adjustments proved to be complex and time-consuming, delaying the availability of the SCR-517A sets.
- Production Delays:
- Initially, Western Electric was contracted to produce 10 sets in February 1942, with a ramp-up to 20 sets per month in the following months. However, these targets were not met. The production schedule had to be revised multiple times, leading to significant delays in delivering the radar systems to the U.S. Army Air Forces (AAF), Navy, and the British.
- Material Shortages:
- The production delays were further exacerbated by shortages of critical components such as the spinner mechanism, which was initially produced by General Electric but later required additional manufacturing by Philco due to supply constraints.
Allocation and Use
Navy vs. Air Force Needs:
- The Navy’s demand for 100 SCR-517A sets for installation on subchasers added further pressure to the already strained production efforts. The AAF agreed to allow this allocation on the condition that they first receive their own scheduled 100 SCR-517A sets and additional SCR-520 sets for testing.
Implementation in Aircraft:
- By the end of June 1942, the AAF had only 11 aircraft equipped with the SCR-517A, but these lacked the necessary spinners, rendering them incomplete. By September 1942, despite the target of producing 1,142 sets for the year, only 203 had been delivered, causing operational delays as aircraft remained grounded waiting for radar installations.
SCR-517A Variants:
- As production continued, the SCR-517A was improved with the development of the heavier B version (which included additional beacon and Identification Friend or Foe (IFF) features) and the lightweight C version. These enhancements, while necessary, further delayed production as the designs were updated.
Operational Impact
B-18 and B-24 Aircraft:
- By the fall of 1942, Secretary of War Henry Stimson’s push for ASY radar on patrol aircraft began to yield results. Although the SCR-517A-equipped B-18As served as a stopgap measure, they were soon supplemented by B-24 bombers equipped with the more advanced SCR-517 radar, which offered longer range and better performance.
Formation of SADU:
- The success of the SCR-517A in ASW operations led to the establishment of the Sea Search Attack Development Unit (SADU) to further develop and test ASW tactics and equipment.
Equipment Details
- SCR-517A Radar:
- The SCR-517A radar system featured a 3-foot diameter concave dish antenna mounted behind a dome, replacing the bombardier’s Plexiglas windows on the B-18A. The highly accurate antenna mechanism, known as the spinner, allowed the radar to scan a wide area with a narrow microwave beam. The radar transmitter and receiver were installed in the aircraft’s nose compartment and radio operator’s position, respectively.