Cutting-edge killer drones will not be flying over the world’s oceans any time soon. The Defense Department’s budget proposal for 2017, released on Feb. 9, terminates an on-again, off-again program dating back to the late 1990s that aimed to develop a bomb-hauling robotic jet capable of launching from and landing on the U.S. Navy’s aircraft carriers.

The decision to cancel the so-called Unmanned Carrier Launched Airborne Surveillance and Strike is reflected in the Defense Department’s 2017 budget proposal, released on Feb. 9. The proposal shows a combined $818 million in funding for the UCLASS killer drone program in 2015 and 2016 and, abruptly, no money at all in 2017.

Instead, there’s a new budget line for 2017—a meager $89 million for a so-called “Carrier Based Aerial Refueling System.” In other words: Goodbye, drone death from above. Hello, flying robot gas stations.

Speaking anonymously to various trade publications, Navy officials have confirmed that this drone refueling tanker will harvest some of UCLASS’ most important technologies. In particular, the Navy wants to harness its radio- and satellite-based control system, which helps human controllers aboard an aircraft carrier launch and land the robot and guide it during missions lasting half a day and covering potentially thousands of miles.

“The Navy has already said it wants to develop the airframe iteratively and that the most expensive part of the [development] is creating a system for an aircraft to move on, off and around the carrier,” an official told the news Website of the U.S. Naval Institute.

But the drone tanker won’t primarily carry the weapons or sophisticated sensors that had been planned for the UCLASS robot, nor will the robo-tanker be very stealthy—that is, able to avoid detection by enemy forces owing to its shape and special coating.

It’s possible that, over time, the Navy could add back weapons and stealth, finally producing the killer drone that many analysts, senior military officers and lawmakers have long argued for… and which almost became reality nearly a decade ago. But there should be no mistaking it. The UCLASS cancellation could be a big setback for U.S. air power.

Back in 2006, the Pentagon had a choice. Option one: It could pour potentially hundreds of billions of dollars into a complex, decades-long effort to build thousands of stealthy F-35 Joint Strike Fighters to replace most of the Cold War-vintage warplanes then in service with the Air Force, Navy, and Marine Corps.

At the time, the F-35 was already showing signs of becoming a deadline-missing, budget-busting disaster, but it was still the conservative option, because for all its new features it was still just another manned jet fighter.

Alternatively, option two: military leaders could bet big on a new kind of technology with the potential to totally transform the way the United States wages war from the air. A killer drone—a small, speedy, pilotless warplane that, its proponents claimed, could be more effective and cheaper than any traditional fighter such as the F-22 or the F-35 could ever be with a person in the cockpit.

Those killer drone prototypes—Boeing’s X-45 and Northrop’s X-47—both sported a single engine and a futuristic diamond-shaped wing around 40 feet in span. And they surprised their developers in early tests. Guided by a combination of human controllers and their own sensors and internal algorithms, the drones proved they could swiftly penetrate enemy defenses.

Small in size, they were hard for the enemy to detect at first. And flying in “swarms” of multiple drones, once detected they could absorb enemy fire, sacrificing a few individual machines as they fought their way to the target.

And since the drones didn’t rely on a human pilot with perishable cockpit skills, the military could mostly keep them in storage until a war broke out. The robots’ operators would maintain their own control skills using computer simulations and the occasional live flight. Eliminating the need for constant training sorties would save many billions of dollars a year, the logic went.

Effectiveness, efficiency—those were the killer drones’ selling points. But the robot warplanes apparently threatened the pilot-centric cultures of the Air Force and the Navy’s aviation arm. So it should have come as no surprise when, in 2006, the military canceled the killer drone effort.

Venting over the decision, one Boeing engineer—who asked to remain anonymous—blamed the military’s slavish devotion to manned warplanes. “The reason that was given was that we were expected to be too good in key areas and that we would have caused disruption to the efforts to ‘keep F-22 but moreover JSF sold,’” the engineer said. “If we had flown and things like survivability had been assessed and Congress had gotten a hold of the data, JSF would have been in trouble.”

Of course, it’s possible that skittishness on the part of the military’s pilots isn’t the only reason for drone program’s demise. The same conservatism that might cause an aviator to balk at the idea of a pilotless jet fighter could also lead senior officers and bureaucrats to choose a technology they’re familiar with over a new, less familiar one—however promising the new tech might be, in theory.

With tens or hundreds of billions of dollars on the line—and, indeed, the bulk of America’s air power at stake—it’s perhaps understandable that the military would prefer to develop yet another manned fighter than to invest heavily in the world’s first jet-propelled killer drone.

Either way, in a surprising twist in America’s drone history, the Navy swooped in and saved the pilotless plane, investing billions of dollars to continue its development under the guise of the aforementioned UCLASS program.

Northrop built a pair of enlarged X-47Bs for testing, culminating in a dramatic series of carrier launches and landings in 2013. Meanwhile, Lockheed, Boeing and General Atomics—the latter the manufacturer of the iconic Predator drone—prepped their own, improved killer drone prototypes, eyeing an eventual contest to produce a war-ready, final design.

In one at-sea trial in July 2013, an X-47B detected an anamoly in its own navigation computer while approaching a carrier and, all on its own, made the decision to divert to an airfield on land. The self-diagnosis was a startling reminder of the robot’s rapidly improving artificial intelligence.

The killer drone seemed all set to join the Navy’s air wings in just a few years. The sailing branch’s plan, until the current budget cycle, had been to pick a contractor in the next couple of years and begin deploying the new drone in the early 2020s, at first complementing then, perhaps eventually, replacing F-35s and other manned planes.

The timing seemed prescient, as the F-35 had run into serious technical and management problems and was years late and tens of billions of dollars over-budget. Of the F-35’s three variants, the Navy’s F-35C version lagged the farthest behind. The UCLASS killer drone seemed poised to finally achieve the air-power coup over manned planes that it came close to achieving back in 2006.

But that was not to be. “We don’t have enough money to do everything we want to do,” Deputy Defense Secretary Bob Work, once a strong proponent of the UCLASS killer drone effort, told trade publication Breaking Defense. Unless Congress intervenes, the current budget proposal unceremoniously ends UCLASS and grounds Northrop’s X-47B and its rival drones in their present forms.

It almost goes without saying that the five-year budget plan also adds more than a billion dollars for 13 extra F-35Cs, despite the plane’s longstanding problems.

Now the Navy will have to make do with a robotic tanker plane, while the F-35—once again victorious over its arguably more capable autonomous foe—dominates the military’s planning and spending. Drone revolution, deferred.