The weapon itself measured 8 feet, 4 inches long, with a body diameter of 2 feet, 3 inches, and a wingspan of 5 feet, 2 inches. It was powered by a Williams International F-121 turbofan that produced 70 pounds of thrust, propelling a total weight of 430 pounds. This combination led to a platform that could remain airborne for a claimed 80 minutes as it loitered over an area waiting for radar arrays to come online.

This 80-minute loitering time, if achieved, could allow a pack of Tacit Rainbow missiles to loiter over a target area for an hour and twenty minutes, engaging radar arrays as they came online or simply forcing the enemy to keep them offline. In either case, it would allow more than sufficient time for friendly aircraft to accomplish their missions inside the target area. 

Although it began as a ground-based weapon system, Tacit Rainbow’s focus soon turned to the skies, with plans to deploy the weapon in large numbers from B-52s, or in smaller numbers from Navy A-6E Intruders, and Air Force EF-111s and F-16s.

“Tacit Rainbow searches hostile territory for radar emitters while entering a target area. If radars are not active, the missile will enter a loiter pattern over the target area. Once a signal is detected, Tacit Rainbow attacks. Should the target be turned off, the missile returns to loiter in the target area, searching for it or other radar emitters.”

Air Force description of Tacit Rainbow upon its unveiling to the public in 1987.

The weapon’s total range has still yet to be released, though its specific inclusion in correspondence between Soviet Minister of Foreign Affairs Eduard Shevardnadze and U.S. Secretaries of State and Defense at the time, James Baker and Dick Cheney, respectively, does offer some insight. 

While Tacit Rainbow was never intended to carry nuclear payloads, the Soviet military believed it could be modified to do so, and as such, wanted it included in the limitations the two nations sought to place on air-launched cruise missiles. Baker countered and won in a letter listing his reasons it shouldn’t be included, third of which addressed the issue of range–which he characterized as greater than 373 miles but less than 500.

“Third, on your concern about range. I am advised that its range is less than 800 km. As you know Tacit Rainbow only became an issue when we considered accepting your proposal for a 600 km ALCM range threshold. Under our preferred position of 800 km, Tacit Rainbow was not an issue.”

-Secretary of State James Baker III in a letter to Soviet Minister of Foreign Affairs Eduard Shevardnadze dated May 19, 1990.

Some unconfirmed sources claim Tacit Rainbow offered a total range of only 280 miles, though if true, that figure may represent the weapon’s actual (and seemingly poor) performance in testing, rather than its intended performance on paper.

“They don’t know ordnance engineering.”

On June 30, 1988, one year after the program was unveiled to the public, the Los Angeles Times published one of numerous stories to come about the cost overruns and program mismanagement that seemed to pervade every facet of Tacit Rainbow’s development. 

According to the report, Tacit Rainbow was already a year behind schedule and ten times more expensive than originally intended, placing a great deal of the blame on Northrop’s shoulders and seemingly shining a light on a conflict between the Air Force and Navy, who were working together on the effort under congressional recommendation. 

“At one point, development costs at Northrop were running $20 million per month,” one official said. “Even the Air Force wanted to terminate Northrop’s contract.”

“Paisley Halted Experts’ Attempt to Kill Missile : Navy Weapons Scientist Who Opposed Troubled Northrop Project Was Later Eased Out of Job” by Ralph Vartabedian in the Los Angeles Times, June 30, 1988

The article also claimed then-Assistant Navy Secretary Melvyn R. Paisley exercised undue influence over the program, going so far as to force seasoned experts out of their jobs at the China Lake Naval Weapons Center for expressing concerns about its troubled development. Those experts, the article contends, could see that Tacit Rainbow was not living up to expectations as early as 1985, with many calling for Northrop’s contract to be terminated in favor of soliciting new bids from defense contractors.

“There was an awful lot of dumb engineering by Northrop,”  said Dr. Frank Cartwright, a former senior adviser at China Lake during Tacit Rainbow’s development. 

“They don’t know ordnance engineering.”

Other allegations of corruption reached Senator Nunn, prompting the aforementioned Op-Ed in his defense, but the trouble for Tacit Rainbow was only beginning. The Navy soon pulled out of supporting full-scale production of the weapon, and an issue of “Inside the Pentagon” printed in November of the following year indicated that the Navy remained hesitant to support production even amid renewed pressure from the Pentagon. 

In February of 1991, the New York Times reported that the Defense Department was canceling Tacit Rainbow as a part of its FY1992 budget proposal, and the following month, a damning report from the United States General Accounting Office would serve as the first post-mortem analysis into the program’s failure. 

The GAO report was the first official document to be released that put Tacit Rainbow’s failings in clear, easy-to-understand terms. To put it bluntly, the weapon simply couldn’t do what it was designed to do. In fact, it could barely find a target at all. 

“Tacit Rainbow was unreliable in its flight test program and did not demonstrate its readiness to begin production. In over one-half of the 16 flight tests, the missile did not hit the target because of guidance system failures and other performance problems, and only 2 successful flight tests occurred out of the last 10 attempts,” the report explained.

Could the U.S. use a new Tacit Rainbow?

In hindsight, it’s clear that the Tacit Rainbow program was too riddled with failures and rampant politicking to have manifested in a successful weapon system, but the concept behind the weapon remains as viable today as ever. 

Perhaps influenced by Tacit Rainbow, the United States would go on to deploy drones into Iraqi airspace at the onset of the Gulf War in 1991 to tempt Iraqi commanders into activating their air defense radar systems. Once online, these systems became easy prey for fighters armed with anti-radiation missiles following behind, but as many stories out of the Gulf War clearly show, surface-to-air missiles remained a prevalent concern.

In 1995, the Pentagon took another swing at a loitering air defense suppression munition with the ADM-160 MALD (Miniature Air-Launched Decoy)

Today, the United States Navy is in the early stages of production on the AARGM-ER, an anti-radiation missile with an operational range of (potentially) around 120 miles. This is just far enough to keep the aircraft employing these weapons out of range of being shot down, but with an increased focus placed on anti-stealth defenses in nations like Russia and China, Wild Weasel F-35s would still face daunting risks in a large scale fight. 

However, in the years since Tacit Rainbow was canceled, drone and missile technology have both improved dramatically. 

It stands to reason that a modern version of the Tacit Rainbow concept, leveraging the low-observability and low-cost of attritable drone programs like the Kratos Valkyrie and even the hypersonic approach and subsonic loitering capabilities from programs like the Army’s Vintage Racer, could wreak havoc on even the most advanced enemy air defenses. 

During Tacit Rainbow’s era, the enemy radar systems had to stay online until the missile reached its target for success, but the AARGM-ER’s targeting apparatus, made up of a digital passive radar emission detector, active millimeter wave radar, and a combination of INS and GPS systems, allows for continued pursuit of radar arrays even after being powered down or potentially, while moving. It goes without saying that a loitering munition equipped with the same targeting capability could be much more effective than even Tacit Rainbow’s unrealized goals.

Even without a hypersonic approach to a target area, a large volume of inexpensive loitering anti-radiation missiles like Tacit Rainbow could overwhelm surface-to-air missile systems without the extended presence of Wild Weasel fighters braving not just inbound SAMs, but anti-aircraft fire and any number of other threats that could arise in a large-scale peer-level conflict. Instead, Wild Weasel could become a phrase more commonly associated with a class of inexpensive swarms of loitering weapon systems, rather than fighters at all. And because these weapons are much smaller than traditional fighters and produce much less heat from their engines, they’re also less likely to be shot down while they wait. 

Like Vintage Racer, the next generation Tacit Rainbow could lob sub-munitions at targets as they appear, saving itself for further missions, or it could potentially fly armed with its own warhead to engage a final target itself after its submunitions were all expended, not unlike the intent behind the otherwise utterly insane Project Pluto. 

Then again, Tacit Rainbow’s development continued for years before the public became aware of its intent or its troubles. Maybe a spiritual successor has already managed the same feat, coming to fruition behind a curtain of classified funding.