Despite its designation, the EA-6B was not a conversion of the A-6B, which was a defense suppression attack aircraft. Instead, the EA-6B Prowler was a four-seat electronic warfare aircraft designed to jam and deceive enemy radar and communications facilities. In later versions, it had the ability to fire HARM missiles against radar sites.
The first EA-6Bs were delivered to VAQ-132 in July of 1971. The squadron flew ECM support for aircraft carriers in the Gulf of Tonkin and the unit entered combat for the first time in July 1972 with VAQ-131 aboard the USS Enterprise. Two Prowler squadrons were active during the Vietnam conflict, and they carried out 720 combat sorties over North Vietnam. No Prowlers were lost in combat during this time.
The ICAP II was a further improvement to the Prowler. The last pre-production Prowler (BuNo 156482) served as the developmental aircraft for the ICAP II and flew for the first time on June 24, 1980.The ability to carry and launch the HARM antiradiation missile was incorporated with the 111th production article, and was retrofitted to earlier aircraft. The weapon's control panel was located at the right front navigator's position. Deliveries of the ICAP II Prowler began with the 99th production machine in January of 1984. All surviving ICAP I and ICAP Mod 1 aircraft were brought up to ICAP II standards.
The next phase was known as "Block 89A", and included an upgrade of 69 Block 82 and 56 Block 89 aircraft. The first of four upgraded Block 89A EA-6Bs flew at Northrop Grumman's St. Augustine, Florida facility on June 8, 1997. It is intended that the entire EA-6B fleet will be upgraded to Block 89A standards before the ICAP III modifications are made.