A 1956 requirement for a low-level, long-range strike aircraft for service with the US Navy produced 11 design proposals from which, in December 1957, that by Grumman, the G-128, was adopted.  Born of the Navy's experience in the Korean War, the new aircraft was to have a high subsonic performance at tree-top height to permit under-the-radar penetration of enemy defences and be capable of finding and hitting small targets in any weather.

     Deliveries to the first Navy squadron to operate the Intruder, VA-42, began on February 1, 1963, and VA-75, VA-85 and VA-65 were among the Navy units soon trained by VA-42 to fly the A6A.  The first Marine Corps unit to become operational on the A-6A was VMA(AW)-242, at NAS Cherry Point in October 1964.  In July 1965, VA-75 began operating in support of US forces in Vietnam, flying initially from USS Independence, and both Navy and Marine Corps squadrons were heavily engaged throughout the remainder of that campaign.  Source: United States Navy Aircraft since 1911 by Gordon Swanborough and Peter Bowers)