The Achilles Heel of the Douglas B-66 Destroyer

The B-66 Destroyer ended up only resembling the A-3 Skywarrior

In January 1952 when the US Air Force issued its official General Operational Requirement (GOR) for a tactical bomber and reconnaissance jet aircraft to replace the Douglas B-26 Invader and the "interim" Martin B-57 Canberra, the selection of a minimum change version of the Douglas A3D Skywarrior as the B-66 Destroyer made sense. Douglas's proposed changes weren't all that major- deletion of the folding wings, catapult gear and arresting gear, addition of ejection seats and anti-icing, strengthening the airframe for the stresses of low altitude flight and an enlarged search radar antenna. Since the aircraft was "off the shelf", no prototypes were ordered. Eventually the USAF's GOR evolved to cover four distinct versions- the B-66B, a nuclear capable bomber version to replace the North American B-45 Tornado, the RB-66B, an all-weather day/night reconnaissance version, the RB-66C, a tactical electronic reconnaissance aircraft, and the WB-66D weather reconnaissance aircraft. Douglas agreed to an ambitious timetable to get the B-66 in production and operational, but the USAF kept requesting changes that ended up making the B-66 Destroyer a totally different aircraft that literally shared nothing in common with the Skywarrior. It's a testament to Douglas's abilities that the schedule slipped only two years as a result of constant changes being requested by the USAF! The B-66 ended up weighing just over 10,000 lbs more than the A3D Skywarrior as a result of all the changes. 

Had it gotten the J57 engine, the B-66 might have had a longer career

But being overweight wasn't the biggest flaw in the B-66 design. Ed Heinemann and his Douglas team recommended the Pratt & Whitney J57 turbojet for the B-66 after the A3D was switched from the anemic Westinghouse J40 turbojet to the more powerful J57 (the first production turbojet in the world to exceed 10,000 lbs of thrust). However, the Air Force held a competition for the engine to power the B-66- in addition to the recommended J57 engine, the Allison J71, General Electric J73 and surprisingly the Westinghouse J40 were submitted. Not surprisingly the J40 was dropped early on and the J73 soon followed for technical reasons. To the surprise of Douglas, the USAF then selected the J71 for the Destroyer, not only an engine that had yet to fly but it was also less powerful than the J57 by nearly 2,000 lbs of thrust! The official reasoning was that the Allison J71 was readily available (a bit of a stretch here on the part of the USAF) and the B-66 had lower priority than other USAF programs that used J57 engines- namely, the Boeing B-52 Stratofortress, the Boeing KC-135 Stratotanker, the North American F-100 Super Sabre, the McDonnell F-101 Voodoo, and the Convair F-102 Delta Dagger. At the time the Voodoo was under development as a long range penetration fighter for SAC, so it became obvious to many that SAC dominated the USAF budget and would receive any and all J57 engines possible. The main reason the F-100 got any J57s at all was that the F-100 was central to the Tactical Air Command's desire to have its own tactical nuclear attack force built around the F-100. 

Ordinarily those assigned to the B-66 Program Office at Wright Patterson AFB would have pushed for the J57, but politically the B-66 was seen as primarily a reconnaissance aircraft and only in interim bomber. Those with fighter experience in TAC wanted the F-100, those with tactical bomber experience in TAC wanted the Martin XB-51. And SAC was determined to preserve its budgetary allocation at all costs. In the end, no one really fought for the B-66 Destroyer when it was given the clearly less-powerful Allison J71 engine. Allison had trouble getting the J71 prototypes bench tested to at least 50 hours without any problems and only barely made the cut which exacerbated the schedule slippage of the first operational Destroyers. And even at that, the test pilots at Edwards AFB flying the first B-66s hated the J71- it was slow to spool up for more power, it surged often, and even would flame out and stall while taxiing. On 8 October 1955 the pilots of the AFTC (Air Force Flight Test Center) filed an extremely unsatisfactory report on the J71. The test force concluded that the J71 engine was accepted by the USAF only partially developed and a replacement engine was needed, the preference being for the J57 used by the Skywarrior. It was alleged that on a hot summer day in Denver with a typical combat load, the B-66 Destroyer couldn't even get airborne!

The tail guns were soon removed and replaced with ECM tailcone

Unfortunately for the B-66 program, the Secretary of Defense at the time, Charles Wilson, came to the Defense Department as the CEO of General Motors, of which Allison was one of its divisions. Wilson's 1953 confirmation hearings before the Senate were highly controversial because of his reluctance to sell his GM holdings and comments that alluded to him possibly favoring GM as Secretary of Defense. The loss of the J71 contract would have been a severe blow to Allison at the time. As a result, the Destroyer kept the J71 engines and Allison tweaked the engine further to bring the engine up to 9,700 lbs of thrust. While this satisfied the USAF given the mission profiles of the Destroyer in the 1950s, the addition of heavy electronic warfare equipment to the Destroyer to created the EB-66, the only tactical electronic warfare aircraft available in Vietnam, strained the limits of the J71 in the hot tropical environment of Vietnam. Destroyer crews nicknamed the aircraft "The Airplane with One-Way Engines" in reference to the fact that outside of the lackluster McDonnell F3H Demon, the other design to use the J71 was the Northrop Snark cruise missile. However, in 1956, Northrop switched the Snark's engine from the J71 to the- you guessed it- J57. 

Source: Glory Days: The Untold Story of the Men Who Flew the B-66 Destroyer into the Face of Fear by Wolfgang W.E. Samuel. Schiffer Military History, 2008, p24-38.