The revolution in unmanned aerial flight has advanced quickly and in dramatic leaps, perhaps none more momentous than the historic landing of an autonomous Navy drone on an aircraft carrier.

That happened for the first time two years ago, when Northrop Grumman’s X-47B, which looks more like a UFO than a military aircraft, took off and landed on the USS George H.W. Bush.

It made history again last year, when it flew alongside F/A-18 fighter jets, the first time a drone flew in concert with piloted planes off a carrier. And later this month, the X-47B is expected to attempt what would be another aerial triumph: refueling midair by a tanker plane.

But despite those breakthroughs, some powerful members of Congress and leading military think tanks say the Pentagon is being too cautious in its development of a technology that they think could push the boundaries of unmanned flight—and the future of warfare.

In what has become a made-for-Washington drama, a group of Congress’ most influential members are pushing the Pentagon to develop what to some sounds like sci-fi fantasy: drones that could not just take off from carriers, but fly for days at a time, covering hundreds, if not thousands, of miles, and perhaps most importantly, haul a hefty arsenal of bombs deep into enemy territory.

That might sound like a tall—and expensive— order, especially at a time when congressionally mandated budget caps are forcing the Pentagon to balance wish lists against necessities.

But proponents of a more ambitious approach, including Sen. John McCain (R-Ariz.), fear that the Navy’s plan to primarily use the drones as eyes in the sky designed to fly around the carriers and detect incoming threats, is misguided. Potential adversaries have developed advanced anti-ship missiles, pushing aircraft carriers well off shore, beyond the striking distance of piloted fighter jets, such as the F/A-18 and the F-35 Joint Strike Fighter.

To counter that, the carriers need stealthy, unmanned aircraft that can fly long distances, in a combat environment, they say. Without that ability, the U.S.’s long-held air dominance is lost and its fleet of aircraft carriers, long a symbol of the U.S.’s ability to project power from wherever, whenever, is at risk of obsolescence.

“If you take the most elementary missiles the Chinese have developed they have already pushed our carriers to a standoff of about 1,000 miles,” said Rep. J. Randy Forbes (R-Va.). “If our carriers get set back that far the F/A-18 and the F-35 are not going to get us where we need to go.”

In a letter last month, McCain, chair of the Senate Armed Services Committee, urged Defense Secretary Ashton B. Carter “to ensure that the Navy’s first unmanned combat aircraft is capable of both providing persistent ISR [intelligence, surveillance and reconnaissance] and conducting strike missions from the carrier at standoff distances in contested environments.”

But defense consultant Loren Thompson said that if the program becomes too expensive, the Navy might decide it can’t afford to pursue it.

“If you ask for too much, it either won’t work or it will be the size of a B-52 Bomber,” he said. “Every time Congress tries to add another requirement to this program, it undercuts support in the Navy for what was supposed to be a relatively modest effort.”

He also said that the Pentagon has plenty of aircraft that can attack from long distances, and noted that it is close to awarding a contract for what’s known as the Long Range Strike Bomber, which would have nuclear capabilities.

Last year, Congress held up funding for the X-47B program until the Pentagon figures out what it exactly it wants. And now the Defense Department is doing a review that would determine whether it should be able to strike at long distances or primarily a surveillance aircraft.

Bryan Clark, a senior fellow at the Center for Strategic and Budgetary Assessments, predicted that the review would find that there are “a lot of other aircraft that can do surveillance around the carrier.”

While creating a drone that can fly long distances, while also carrying a heavy weapons payload, sounds like a massively complicated endeavor, he said that the X-47B “has been so successful it seems like building an aircraft like that is not as risky a proposition as we had thought.”

Forbes said he was glad the Pentagon was taking a deliberate approach. The decision it makes “will lock us in to the direction we will go for the next 20, 30 years,” he said. “That’s why it’s so important …we make the right decision now.”

A U.S. Navy video from August 2014 shows testing of an unmanned aircraft aboard the aircraft carrier USS Theodore Roosevelt. (Video courtesy U.S. Navy)