The Douglas finished B-66 ‘Destroyer’ was a light bomber based on the United States Navy's A3D Skywarrior, and intended to replace the A-26 Invader. Deliveries of the Aircraft started in 1956, and 145 of this model were produced. They were used as the major night photo-reconnaissance aircraft of the USAF.

The Air Force actually bought the B-66 for lack of any better choice. The B/RB-66 was to be an interim weapon, primarily earmarked for tactical reconnaissance. The Air Force requirements proved too ambitious, too hasty, and the B-66 program fell behind schedule. 

Exacting requirements given by the USAF were levied which, in view of the program's urgency, proved totally unrealistic. The future B-66 Destroyers, as the Air Force versions of the Navy aircraft were designated, had to be fast, highly maneuverable, and able to perform in all types of weather, at very high or low altitudes, and from makeshift or short runways. The B-66s also had to have a 1,000 nautical mile radius and be large enough to accommodate a 10,000 pound payload of either atomic, conventional, or photographic flash bombs. The bomber and reconnaissance versions were to be kept closely alike. Moreover, all versions of the aircraft were to be fitted with sophisticated electronic countermeasures components to deal with enemy radars.

72 of the B-66B bomber version were built, 69 fewer than originally planned. Thirteen B-66B aircraft were modified into EB-66B electronic countermeasures aircraft for the Vietnam War. Unlike the A-3 which performed some bombing missions, the Destroyer was not used as a bomber in Vietnam.

Based on a proposal by Douglas, the Air Force in 1952 bought the Navy's A3D-1 ‘Sky Warrior’. Douglas later removed folding wings, catapult capability, and arresting gear from the Navy MD configuration. In keeping with Air Force instructions, adaptations were kept to a minimum in order to accelerate the issues. Also, in addition of upward ejection seats were installed. But once these changes were made, new requirements emerged, as did design and layout deficiencies. Later, larger tires were provided, as were emergency air brakes, wing spoilers, and improved lateral controls. The wing's angle of occurrence was changed to minimize ‘dutch roll’ and the cockpit pressurization was enhanced. 

In June 1954, the first RB-66 flight flew. It was an unsuccessful flight. The aircraft did not handle well, it pitched up unexpectedly, the wings vibrated excessively, the vision from the canopy was poor, and the landing gear doors did not function properly. 

In 1955, the B-66 program was retained, but reduced as no aircraft were available to substitute it. The manufacturer did some improvements before it entered operational service in 1956, permitting the long overdue replacement of the obsolete RB-26s, and allowing phaseout in early 1957 of the problem-ridden RB-57As. 

In the same year, 294 instead of the 342, B-60 aircraft initially programmed, was assigned for the Tactical Air Command (TAC), some of the badly needed reconnaissance models promptly joined the Pacific Air Forces in the fall of 1956. Others went to the United States Air Forces in Europe in late 1957. Their successive engines, Allison J71-A-9s and J71-A-1 were better, but not good enough, and the subsequent retrofit of more powerful J71-A-13s caused other problems. Every version of the aircraft remained wearisome. 

In the long run, the B-66s became a main asset of the Air Force intelligence gathering and electronic warfare forces. Even though lack of money precluded numerous special modifications and most modernization projects, many changes were effected as the aircraft's specialized roles accrued. Because of the US involvement in Southeast Asia, the aircraft's life-span was extended. After refurbishing, the aircraft, now known as the EB-66, headed for the war theater. Other B/RB-66s, although earmarked for retirement, were kept active, re-equipped, re-designated, and committed to combat as early as 1965. In 1966, press accounts began to give the EB-66s credit for neutralizing surface-to-air missile radars as well as much of the enemy's radar-controlled but conventional anti-aircraft weaponry. As the war escalated and enemy defenses grew, the old aircraft, with their upgraded electronic devices and despite their worn-out engines, became invaluable and so remained until the end of the conflict. Thus, a difficult decision, made nearly 20 years before by a greatly concerned and cautious Air Staff, proved correct.

In the early 1950’s, while the Air Force hoped that the awaited B-66 would replicate the A3D, the new aircraft's basic configuration was being worked out. Not yet incorporated were a few major changes proposed by Douglas. The difficulty of these basic modifications could be disputed. The first step was to delete from the Navy A3D the various inherent features of a carrier-based aircraft, such as folding wings, catapult capability, and arresting gear. Satisfying the stated Air Force requirements came next, keeping in mind that only a minimum of adaptations could be tolerated in view of the program's urgency. Essentially, this meant that upward crew ejection seats had to be installed, since one of the aircraft's many roles would be to fly at low altitudes and at fairly high speeds. In the same vein, the airframe structure had to be strengthened to compensate for the greater stresses of low-altitude, high-speed operation. Finally, a 45-inch search radar antenna needed to be substituted for the 30-inch antenna of the A3D. These changes were the salient points of the basic configuration approved by the Air Force in May 1952. While they brought the airplane closer to the Air Force's tactical requirement, they reduced range from 1,325 to 1,070 nautical miles.

The Air Force from the start had planned to define further the actual configuration of the new aircraft's bomber version. The Air Force nevertheless wanted the aircraft to be interchangeable, and every effort was to be made to keep the bomber and reconnaissance versions closely alike. And, while going along with the so-called major changes of the approved configuration, it had been busy identifying necessary minor improvements. Under this category fell the exchange of Navy- for Air Force-designed equipment, a substitution which would simplify the airplane's logistic support. An unexpected jolt, however, was the snowball effect of the changes introduced in the approved basic configuration.

Also, new requirements kept showing up, as did design or layout deficiencies. By mid-1952, the quasi A3D that the Air Force hoped to rush into production had acquired a long list of innovations. The Air Force did not like the A3D's hydraulic system and wanted the system to be completely revised. It wanted the aircraft's fuel system to be redesigned and insisted that the B/RB-66 should carry a fuel purge system, a feature missing from the A3D. Finally, all B/RB-66s were to be fitted for in-flight refueling, the photo/navigator station had to be relocated, and better engines were needed.

As anticipated in late 1951, engine difficulties were materialized. Development of the Westinghouse J40-WE-5, due to equip the Navy A3D, was not progressing well. This confirmed the Air Force's suspicion that such an engine would be unable to give the B/RB-66s the radius of action and overall performance required of the airplanes. An engine competition, initiated by AMC, yielded several possibilities. 

Westinghouse offered a new version of the J40, which was turned down because of excessive fuel consumption and because the engine's 7,250-pound thrust was minimal, when compared to the 9,750 pounds of the J71 engine proposed by Allison, a division of the General Motors Corporation. The General Electric J73 failed because of its cost and the fact that its development lagged behind the J71. In addition, and perhaps of greater significance, General Electric at the time was fully occupied with the J47 engine program. Douglas Aircraft favored the Pratt and Whitney J57, but because it was earmarked for several weapon systems of higher priority than the B/RB-66, the Air Force, did not feel the manufacturer could produce enough J57s to satisfy all demands. The J75 was subsequently selected by the Navy to replace the MD's J40s. This left Allison's J71 as the undisputed winner of the competition. Yet, even though Allison had guaranteed the development status of its engine, problems in getting the J71-A-9 engine through its 50-hour test held back the Air Force production order until 5 August 1952, 2 months later than required in order to maintain the aircraft's schedule lead time. In fact, AMC authorized the engine's production before completion of the 50-hour test, a risk frowned upon by the Wright Air Development Center.

For many years after its introduction, it was also the heaviest aircraft ever flown from an aircraft carrier, earning it the unofficial nickname "The Whale". Its primary function for much of its later service life was as an electronic warfare platform and high capacity tanker. The EA-3B model was modified for electronic intelligence against the Warsaw Pact. Missions were flown around the globe beginning in 1956, with the B-47 flying a similar mission. It carried a crew of seven, with flight crew of three in the cockpit and four electronic systems operators in the converted weapons bay. It offered unique electronic reconnaissance capabilities in numerous Cold War-era conflicts and the Vietnam War.