The forerunner of the AN/SPS-40, the AN/SPS-31 (XN-1), was developed starting June 1956 by STAVID Engineering. This radar system was determined to be too large for use in the
Fleet Rehabilitation and Modernization (FRAM) program for WWII-era destroyers undergoing modernization. The SPS-40, which used numerous off-the-shelf parts, was proposed as an alternate by
BUSHIPS as a suitable radar design for the FRAM program. The CNO directed procurement, in advance of service approval, on 10 March 1959 to meet the schedule for the FRAM program and provide the radar frequency diversity required by OPNAV. Development and production were conducted simultaneously. A separate Technical Evaluation, normally conducted in the contractor's plant, was not performed due to the compressed development schedule. Instead, BUSHIPS requested CNO approval for a concurrent Technical and Operational Evaluation. The equipment was installed in the in August 1961, and the evaluation was conducted by COMOPTEVFOR between September and November, 1961. After some deficiencies were corrected, the SPS-40 was accepted for service use in May 1962. The AN/SPS-40B radar set was developed as part of the DART program to improve reliability compared to earlier versions of the SPS-40. It was installed on the s, as well as the s and the
Tarawa-class amphibious assault ship. The SPS-40 and SPS-40A were also upgraded to SPS-40B standard, creating the SPS-40C (from SPS-40) and SPS-40D (from SPS-40A). ==Variants==