The Compelling Case For Turning S-3 Vikings Into The Navy’s New MQ-25 Tanker Drone

There’s plenty of paid for S-3s that can be converted to do the job and a dedicated Viking tanker variant has already been engineered and flown.

byTyler Rogoway|
MQ-25 photo


The Navy's Carrier-Based Aerial Refueling System (CBARS) initiative, now commonly referred to as the MQ-25 Stingray program, has heated up, and all three competitors have unveiled their proposed unmanned tanker designs. But considering the dwindling ambitions and ever-lengthening timelines that have plagued the Navy's initiative to field a drone of any kind for its carriers, one has to question why the service needs a purpose-built tanker drone at all, especially considering that a potentially far more economical and faster solution may have been quietly baking in the Arizona sun for nearly a decade.

The idea of retooling the mothballed S-3 Viking fleet into unmanned drones popped up in a twitter conversation recently on our friend Stephen Trimble's page. At first, I had the feeling of deja-vu, but then I remembered I proposed doing just that six years ago and brought it up again two years later.  

VX-30 was the last Navy unit to operate the S-3. They used jets for range clearing and monitoring duties as well as for test various subsystems. , Tyler Rogoway/Author

The fact of the matter is the Pentagon still has 108 S-3 Vikings serving as rattlesnake shades down at its boneyard in Tucson, Arizona. 83 of those are S-3Bs, 10 are S-3As, and 15 are ES-3As. 

The Viking was controversially retired from service in 2009, with a handful of jets continuing to serve in support roles till 2016. NASA is now the last S-3 operator, having a lone S-3B that works as a test platform out of the Glenn Research Center. 

The last Vikings: The final four S-3s still flying at the time sat together on the NAS Point Mugu ramp back in September of 2014. Now just NASA's jet remains in the air. VX-30 lost their beloved S-3s not because the jets had issues, but because the Navy didn't want to pay to put them through scheduled depot maintenance. , US Navy

The thing is that the average S-3 in storage has half its life still left in it. The airframes were cleared to operate out to a whopping 18,750 hours. Their engines are still widely used on various aircraft, including everything from the A-10 Warthog to business jets to regional airliners. And apparently, there are a lot of S-3 spare parts still on hand. 

The aircraft have been available for potential export for years, and South Korea wanted a number of them for a time, although they have since moved away from the deal and are now looking for a more advanced maritime patrol aircraft. 


The S-3B already served the twilight of its career as a tanker, lugging roughly 16,000lbs of gas around while carrying a buddy-refueling pod. But Lockheed once had a far more ambitious plan for the type when it came to the tanker mission. 

An article in recalls this past "KS-3" initiative: 

"One of the first proposed S-3 variants was a tanker concept for in-flight refueling of carrier-based aircraft. Designated KS-3, the dedicated tanker concept consisted of a standard S-3 wing fuel tank and refueling probe but added a conformal weapons bay fuel tank, wing pylon mounted drop tanks and a dual internal hose and reel drogue system. 

The aircraft also included additional dual ground refueling receptacles. This would speed the on-deck refueling turnaround time. The tanker concept also comprised state-of-the-art navigational and communications avionics with provisions for secondary mission capabilities to conduct EW (electronic warfare) and C3 (communications relay) operations. In order to prove the S-3 tanker concept to the Navy, Lockheed proposed developing an operational KS-3 demonstrator aircraft. 

To keep costs down, an existing flight test S-3 Viking was modified into the in-flight tanker configuration. Ship No. 5 of Lockheed's S-3A flight test program was diverted and equipped with a bolt on belly tank (simulating the proposed conformal weapons bay tank) modified wing pylons for 600 gallon drop tanks and a single hose and reel drogue system incorporated into the fuselage.

The designated KS-3A prototype was flown for almost two years and proved to be a remarkably stable and efficient refueling platform. It demonstrated the ability to move large quantities of fuel with a minimum fuel consumption which maximized available fuel for in-flight transfer. During tests, the KS-3A refueled a variety of Navy aircraft. 

With its ability to be replenished itself in-flight using its refueling probe the S-3 could give up more fuel than any other carrier-based tanker aircraft to date. But despite its laurels, the Navy did not buy the KS-3, so none were produced. The modified KS-3A was later used for pilot training by VS-41 before being re-configured as a US-3A COD aircraft."

The KS-3 prototype refuels a US-3A COD Viking derivative. , Photo via

In total, this KS-3 Viking derivative would be able to carry a whopping 30,000lbs of gas—and possibly more today if further modifications were made. The current requirement for the Navy's MQ-25 drone is to be able to fly out to 500 miles and offload 14,000lbs of gas and then safely return to the carrier. In other words, the KS-3 would shatter that requirement. 

By our calculations, an S-3 burns roughly 1,600lbs an hour at cruise. It would take roughly 1.5 hours to reach its station and the same time on the return trip. That is 4,800lbs of gas. Add in an hour of loiter time and margin for launch and recovery, and that totals around 7,000lbs just as a rough estimate. Add an extra 1,000lbs for good measure. That leaves 22,000lbs of fuel to offer to its 'customer' aircraft. 

When you consider all the engineering had been done and paid for decades ago to turn the S-3 into a dedicated tanker, and the configuration has even been flight tested for two years, the risk and costs in doing so now today would be minimal. 

To save even more time and money, and in exchange for a little fuel, the existing Cobham aerial refueling pod could be used under the wing instead of an internal system. In fact, the MQ-25 program requires the use of this pod on any entrants into the tanker-drone tender. 


In addition, an updated KS-3 would still have room for additional capabilities. The MQ-25 tender requires the aircraft have an electro-optical sensor ball, and the S-3B already has such a system that retracts in and out of the fuselage that could be easily upgraded with a new unit. It also has a big radar aperture that is ideally suited for surface search radar. There is also plenty of room for communications relay and satellite communications gear as well, much of which could make use of the jet's existing infrastructure. 

And as the quote above stated, a KS-3 can do what no current MQ-25 entrant can—it can take on fuel in midair itself. This drastically increases its operational flexibility.

As for a concept of operations, an 'MQ-3T' could be optionally manned, being flown by a human during positioning flights, and put to use in an unmanned fashion onboard the carrier and for training missions over designated airspace. 

Alternatively, they could be strictly unmanned, which would provide even more weight and space savings that could allow for even more fuel to be carried. Still, the optionally manned factor could be key to any Navy tanker-drone program's survival—more on that in a moment. 

General Atomics MQ-25 Stingray design., General Atomics

These adapted airframes could leverage all the research garnered from the X-47B program and incorporate that as well as other relevant emerging technologies into their control suites. As for how hard this would be to accomplish, I asked someone who works in this exact space. They said it would be easier than incorporating it into a new drone and would allow for redundancy that would help quickly prove the unmanned concept and the technologies it relies on. 

They also mentioned the QF-16 program as a reference along with other developments in the semi-autonomous unmanned space, like those related to the Navy's MQ-4C Triton program. It's also worth noting that all the competing companies in the MQ-25 tender have semi-autonomous control software and interface experience as well that they could build into the MQ-3T tanker for unmanned operations just like they could with an MQ-25 drone. 


The Navy already blew it by not procuring a multi-role Unmanned Combat Air Vehicle (UCAV) capable of penetrating enemy airspace over long distances as was originally planned. Those programs morphed over the last decade or so from J-UCAS to UCLASS before turning into the non-stealthy tanker MQ-25 program as we know it today—with a few projects strewn in between. 

Because of the Navy's ever-changing requirements and their decreasing fiscal attractiveness to contractors, every entrant into the MQ-25 contest heavily draws upon or is a direct remodel of previous work done for the now-defunct Naval UCAV programs. In other words, none of the MQ-25 competitors are proposing a full-fledged 'clean-sheet' design or even building prototypes of such a design. As a result, there are significant risks with all the bidders' proposals, no matter how much they say there isn't.

The X-47Bs were hugely successful and promising yet in a stunning and laughably illogical move, the Navy stepped away from the concept to procure a dumbed-down tanker instead. The aircraft, or one like it, clearly threatened the F-35C program and manned carrier aviation in general for certain mission sets. , USN

The one company who had put a real flying carrier-based drone prototype through extensive testing and even operated from a carrier and refueled from a tanker with it is Northrop Grumman and their X-47B demonstrators. The company, which was favorited to win by many, dropped out of the MQ-25 contest abruptly last fall. This may have been a very wise decision in retrospect.  

The cost of just going the next step and fielding a proper UCAV over a tanker-drone that will have similar features anyways seems negligible. So the question is why should the Navy spend a ton of money and take on huge risk for a totally new tanker drone when they can potentially reuse a known commodity they already own, one that will likely have more flexibility and capability from day one than the alternative? 

The service can proceed with procuring a family of advanced unmanned combat aircraft systems, including a tanker capability, while the refitted S-3s prove the concept of carrier-borne drone operations. And above all else, under such a plan, the Navy can field a tanker capability in a far quicker timeframe than what the current MQ-25 program currently proposes.


When it comes to risk, the S-3s are essentially free. If they end up in the water during the unmanned carrier operations teething process, oh well, it's a cheap price to pay for proving a game-changing technology and providing a needed capability to the fleet. Dumping high-tech drones that cost tens of millions of dollars into the sea, on the other hand, would be a scandal and could the essential future of unmanned carrier operations in doubt. 

As of 2014, there were 87 S-3s that could be converted for future use according to Lockheed officials. That number has likely gone up as the final three Navy S-3s have since been retired, some of which were the best of the lot. At the very least, 90 aircraft are available for conversion and Lockheed said it would support those jets throughout their service lives if they returned to flight—well that's what they said before they were competing for the MQ-25 unmanned tanker contract. 

Some of the Vikings stored at AMARG., Google Earth

Considering just four aircraft based on the MQ-25 winning design will be built before the Navy decides if it will order a total of 72 aircraft, there are plenty of S-3s to satisfy this requirement. As we mentioned before, the beauty of using the S-3 is that Navy could obtain its first prototypes far faster than what's demanded under the MQ-25 contract, under which the first four aircraft won't be delivered till around 2023. And that is if everything goes as planned and if the program even survives till then. 

Lockheed's flying-wing MQ-25 design., Lockheed Martin

So in essence, before the Navy spends billions on new MQ-25 tanker drones, they should seriously consider resetting the program to include a family of unmanned systems, namely a penetrating UCAV and closely related tanker, and move immediately to field the S-3 in the unmanned tanker role. 

By having the craft optionally manned it would also have a much better chance of actually making it to operational fruition as by all indications the MQ-25 program, as it sits today, seems to have fluctuating support at best among the pilot-dominated Navy aircraft procurement apparatus. 

With more Super Hornets now on the order books, and a service life extension program spinning-up for the oldest F/A-18E/Fs, the need to offset the tanker role will become less pressing. As such, a cheap, optionally manned, S-3 recycling program of sorts will have a far better chance of surviving, especially if it provides a truncated timeline for fielding an operational capability and reduced costs. 

Although Lockheed would have to be involved in any regenerated S-3 initiative to some degree, the contract to develop the aircraft into an unmanned system and to run the program as the lead contractor can be open to anyone. This is not unprecedented in any way. BAE System ran the QF-4 program and Boeing currently runs the QF-16 program. 

Once the S-3s have done the job of 'bridging the gap' between unmanned and manned carrier aviation, and the new family of advanced unmanned systems is ready in the coming decade, the Vikings can be finally put to rest. 


You may wonder why such an initiative wasn't put into practice, or at least seriously considered already considering the S-3s are just sitting there. Remember, recycling old aircraft into new useful platforms isn't glamorous. It won't provide a windfall of revenue for a defense contractor, nor will it be something a congressman can spike the football with to their constituents. And above all else, it won't be a program that will put extra stars on shoulders of the Navy brass nor guarantee them lucrative jobs at defense contractors once they leave the service. These factors alone are often times why logical gets washed away when it comes to weapons procurement. 

Beyond that, it seems incredibly logical and should be at least carefully examined in an official capacity before the MQ-25 contract is awarded late this Summer.  

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