Officials intended for the aircraft to be a simple development of the earlier A-3, taking advantage of being strictly land-based to dispense with unnecessary naval features.

Further variants of the type were developed, leading to the aircraft's use in signals intelligence, electronic countermeasures, radio relay, and weather reconnaissance operations.

It was recognized that the type was capable of carrying out mission profiles practically identical to that of the much larger Boeing B-47 Stratojet, operated by the USAF.

This performance, coupled with the fact of development costs having already been paid by the Navy, as well as pressing needs highlighted by the Korean War, made the A-3 attractive to the USAF.

[3] For this reason, no prototypes were ordered when the USAF issued its contract to Douglas in June 1952, instead having opted for five pre-production RB-66A models to be supplied, the aerial reconnaissance mission being considered to be a high priority for the type.

However, aviation authors Bill Gunston and Peter Gilchrist attribute many of the design changes to have been made "merely to be different", being driven by an intense rivalry between the two services.

[7] Gunston and Gilchrist observe of the B-66 that: "The history of the aviation is sprinkled with aircraft which, to save money, were intended to be merely a modified version of an existing type.

[3] On 28 June 1954, the first of the RB-66A pre-production aircraft conducted its maiden flight, development being only slightly behind schedule despite the substantial redesign work involved.

On 4 January 1955, the first production B-66B aircraft, which featured an increased gross weight and numerous other refinements, performed its first flight.

However, the USAF decided to curtail the bomber variant's procurement, cancelling a further 69 B-66Bs and largely relegating the model for use in various test programs.

Accordingly, many examples served with tactical reconnaissance squadrons based overseas, typically being stationed in the United Kingdom and West Germany.

These aircraft were outfitted with distinctive wingtip pods that accommodated various receiver antennas, which were also present upon a belly-mounted blister.

[citation needed] On 10 March 1964, a 19th TRS RB-66C flying on a photo-reconnaissance mission from the Toul-Rosières Air Base in France, was shot down over East Germany by a Soviet Mikoyan-Gurevich MiG-21 after it had crossed over the border due to a compass malfunction.

[citation needed] The Northrop X-21 was a modified WB-66D with an experimental wing, designed to conduct laminar flow control studies.

Northrop began flight research in April 1963 at Edwards Air Force Base, but with all of the problems encountered, and money going into the war, the X-21 was the last experiment involving this concept.

[12] United States Air Force Data from McDonnell Douglas aircraft since 1920 : Volume I[16]General characteristics Performance Armament Avionics The shooting down of an EB-66 over North Vietnam and the subsequent rescue of one of its crew became the subject for the book Bat*21 by William Charles Anderson, and later a film version (1988) starring Gene Hackman and Danny Glover.