The U.S. Navy spent $744 million to develop and build its two Northrop Grumman (NOC -0.38%) X-47B unmanned combat air system-demonstrators (stealthy, carrier-launched drones). Then it consigned the program to the scrap heap.

Northrop Grumman's X-47B program was all ready to take off -- then it got canceled. Image source: Northrop Grumman.

In their place, the Navy now wants to build not just two, but potentially a whole fleet of carrier-launched drones capable of conducting aerial refueling (and maybe doing a bit of surveillance work on the side) for its piloted fighter jets. Initially dubbed the "Carrier Based Aerial Refueling System," or CBARS, the Pentagon recently renamed the as-yet-nonexistent drone aircraft MQ-XX Stingray.

The "M" means multirole. The "Q" designates that it's a drone. And the double-Xes remain to be filled in later. But who will do the filling in?

Will Stingray get a stinger?
Northrop Grumman, once the odds-on favorite to build any combat drone for the Navy following its successful tests of the X-47B, is getting some competition as the UCAS program evolves. As USNI News, the publishing arm of the U.S. Naval Institute, explains, there's a fierce debate going on within the Navy. Forward thinkers advocate building the Stingray as a stealthy, long-range strike drone, armed to the teeth with bombs and missiles, and capable of going places the Navy's F/A-18 fighter-bombers cannot.

More cautious sorts, such as Director of Air Warfare Rear Adm. Mike Manazir,  prefer to relegate drones to a supporting role -- essentially, flying gas stations for fighter jocks -- at least initially.

We've got an idea!
One prominent voice supporting the strike option is Northrop rival Lockheed Martin (LMT -0.42%), which last month came out in favor of designing the Stingray to take on all three of the roles discussed above (tanker, ISR platform, and strike jet). Designing the Stingray as a stealth flying wing, says Lockheed, wouldn't prevent it from being loaded up with aviation fuel and sensors, should the Navy go the more conservative route. On the other hand, should the Navy later prefer an armed Stingray, then the flying wing is stealthier. Gas tanks can be replaced with bomb bays, radar-absorbing coatings applied, and voila -- a stealth combat drone.

Granted, as the maker of both the stealthy F-22 Raptor and the stealthy F-35 Lightning II, Lockheed Martin is somewhat biased toward the stealth option. But Northrop Grumman, too, designed X-47B as a flying wing, and presumably prefers stealth as well.

However, two other likely rivals for a drone tanker contract, Boeing (BA -2.20%) and privately held General Atomics, both argue in favor of more traditional (and less stealthy), potentially cheaper "wing-body-tail" designs for Stingray.

What comes next?
A cautious and cash-constrained Pentagon is likely to give Boeing's and GA's ideas a close hearing when it begins preliminary polling of defense contractors about their ideas for the Stingray later this year. On the other hand, Lockheed Martin (and presumably Northrop Grumman as well) believe that "flying wing" does not necessarily equal "expensive." They'll be making a case for a more robust and evolvable design for the drone.

Which argument wins out (and which defense contractors win contracts) could be decided relatively soon. After sounding out its suppliers later this year, the Pentagon plans to issue an official request for proposals to build the Stingray in 2017, award a contract in 2018 -- and begin first deployment around 2025.

By then, analysts estimate that the annual market for militarized drones could surpass $10 billion -- and Stingrays could make up a good chunk of that.

The X-47B is flying off into the sunset. And now we wonder: What comes next? Image source: Northrop Grumman.