Lockheed Martin has labeled the hypersonic technology to be used in the proposed SR-72 Mach 6 aircraft as the “new stealth.” It is really the old stealth, and it points to a classic example of how almost every military and political leader in Western defense fell in line behind a technical miscalculation.

The story of the SR-72's predecessor, the A-12 Oxcart, is endlessly fascinating. One of its most important and long-concealed aspects was the critical role of stealth. The Skunk Works' Texas rival, Bob Widmer's team at General Dynamics, came close to beating Lockheed for the CIA's business with their stealthy Kingfish, which looked weirdly like the much later F-117. Skunk Works head Kelly Johnson, who had been a staunch skeptic when it came to “radar camouflage,” hurriedly reshaped the Lockheed contender with chines, canted tails and radar-absorbing structures.

Behind both designs was a theory that reduced radar cross-section (RCS) and high speed would combine to defeat surface-to-air missile (SAM) systems. North American was even looking at ways of reducing the head-on RCS of the B-70 Valkyrie heavy bomber.

None of this cut any ice with Robert McNamara, Kennedy's defense secretary. His “whiz-kid” operations analysts believed the Soviet Union would quickly develop bigger SAMs and radars that would wipe out the advantages of height and speed. The B-70 was canceled, and a nuclear-strike version of the A-12 was tolerated only when it was turned into the experimental YF-12 and unarmed SR-71. McNamara's favorite combat aircraft, the F-111, was designed around the ability to fly at Mach 1.2 at low altitude, and that was the only Pentagon-approved formula for a follow-on bomber study that would lead to the B-1.

The problem with McNamara's orthodoxy was that it was wrong. The S-200 SAM and MiG-25 interceptor that the Soviets designed to shoot down the A-12 could not alter the laws of physics. At high altitude, it takes wing area to intercept even a not-very-agile target, and it takes a lot of propellant to loft that big, draggy kill vehicle before the Mach 3 intruder turns the intercept into a tail-chase that the rocket loses.

Johnson's successor, Ben Rich, estimated the S-200 could down an SR-71 only if the warhead was of the instant-sunshine variety. In practice, nobody ever hit a Blackbird, while McNamara's low-fast penetrators proved vulnerable to guns, pelicans and attempts to tie the record for minimum altitude.

The U.S. Air Force dusted off the “high-fast sanctuary” in 1982 in defining the Advanced Tactical Fighter, the program that led to the Lockheed Martin F-22. ATF was intended to cruise at Mach 1.6 and pull 6g at supersonic speed in burner, all at 60-65,000 ft.

The original ATF requirements balanced stealth against speed, height and agility. All-aspect stealth was added to the menu after Lockheed and Northrop promised the Pentagon that the price in weight, money or risk would be small. The USAF would be in better shape today if they had been right. If you want to see the original requirements in action, look at the Chengdu J-20 and Sukhoi T-50.

High-fast made another brief return to the limelight in the early 2000s. Northrop Grumman's bomber studies focused on sortie generation over long distances. A supersonic aircraft cost more than a subsonic design, but could fly more sorties in the same period and deliver the first strike more rapidly. If the goal was to threaten fleeting targets over a wide area, each supersonic aircraft could hold a greater area at risk. One engineer argued, “You need fewer systems, because the question is 'Where can I be in 10 minutes?'”

Is high-fast worth reconsideration now? There are challenges. Speed makes it harder to search for and hit targets on the ground. It's costly, but whether it need be much more costly than a high degree of stealth is an open question. It means reviving investment in forgotten technologies.

The SR-72's Mach 6 goal will be hard to reach. But do we really need to go that fast? Mach 3-4, high altitude, situational awareness, reduced front-sector RCS and good electronic attack might be enough, and we could get there without resorting to ramjets.

But today's bomber studies are focused on stealth, and even the value of the F-22's speed and agility in dodging SAMs is not stressed today because awkward questions might follow concerning the survivability of slower, less maneuverable aircraft with a similar or slightly larger RCS. That is today's orthodoxy, more deeply entrenched than McNamara's faith in hedge-hopping.

As the 19th century humorist Josh Billings put it: “It ain't what a man don't know that makes him a fool. It's all the things he does know that just ain't so.”