Aerial Refueling and Preserving Optionality

Update schedule change: I'm dropping my Friday updates going forward: with my childcare duties and having burned through much of the backlog of items I wanted to blog about, I'll be updating only two days per week: Monday and Wednesday. Now on to the (last?) Friday musing:

Inauspicious Beginning

This post was inspired by poor phrasing: on March 6, 2025, Aviation Week quoted General Randall Reed, the chief of the US Air Force Transportation Command, as stating that for the brand-new B-21 Raider bomber, “it’s going to be a little bit higher requirement specifically in the fuel transfer”. At the time, Aviation Week reported that meant that the B-21 would require a faster fuel-transfer rate, i.e. that a single aerial refueling tanker could deliver X gallons per minute more than it could today. Later, Transportation Command clarified they meant that the US Air Force needed more tanker aircraft, not a faster pump.

I had a whole rant planned on how something had to be horribly flawed because the original refueling requirements were based on fuel-thirsty 1950s bombers with 8 engines, so a a 2020s bomber with 2 engines couldn’t possibly need more gallons per minute. But the phrasing was flawed, not the concept. But as bad as the issue is for bomber fleets, the lack of aerial refueling is even worse for fighter aircraft fleets: 

1. Modern Western fighters were optimized for fighting over Europe (small geography) and/or with aerial refueling in mid, so for a given distance they are far more likely to need fuel than a bomber, and 
2. We have two incompatible Western standards for aerial refueling and have avoided the opportunity to harmonize them and all of the tactical options it unlocks.

Aerial Refueling Basics

 

Today I’m focusing on the second item above. Aerial refueling is the passing of fuel from one aircraft to another while both are in-flight. This gives two large advantages:

1. The receiving aircraft can significantly increase its range. In the Falklands War, the British Royal Air Force launched transatlantic bombing raids with medium-range Vulcan bombers in a massive coordinated operation including aerial refueling tankers refueling other tankers to yield the necessary range.
2. An aircraft can take off with a minimal amount of fuel to avoid overloading its maximum takeoff weight.

For aircraft built for the United States and its allies, two mutually-incompatible methods of aerial refueling exist today:

Boom: Used by the US Air Force, it was developed first to support nuclear bombing strikes against the Soviet Union. The most important feature was large gallon-per-minute offload speeds to fill gigantic bomber fuel tanks in a reasonable time. These require a large “tanker” aircraft with a long rigid boom, which prevents small aircraft from serving as tankers. The receiver aircraft has a socket (normally installed in the top-center of the aircraft) the boom locks into during fueling.

Probe and drogue: Used by the US Navy, it was developed so that aircraft carriers could have their own refueling tankers. The most important feature was that the system was compact enough to fit in an existing carrier-based aircraft. The tanker carries a long hose with a shuttlecock-like “drogue” at the end, while the receiver aircraft has a “probe” that it flies into the drogue basket to form a fueling connection. The downside of probe-and-drogue is that it requires a more agile receiver aircraft to successfully fly into the basket, and its maximum fuel transfer rate is lower than boom-type refueling. HOWEVER note that most fighters receive the same rate of fuel from both types of tanker aircraft, only large aircraft like bombers take advantage of the higher transfer rate.

The Challenge

You may have noted that even within the US military, planners have to juggle between different aerial refueling methods. If in 2003 a US Air Force F-15 was supporting a strike on a target in Iraq and was low on gas, it couldn’t get fuel from any of the Navy assets in the area. Similarly, if a Navy EA-18G Growler is supporting an Air Force strike with jamming (because USAF doesn’t have a dedicated electronic-attack aircraft; that’s a different rant), it’s can’t top off from the Air Force’s tankers (unless they’ve installed a special kit).

It gets even worse in joint operations: Canada and the US jointly patrol North American airspace, e.g. intercepting Russian bombers (yes, those patrols still happen), but US F-16s are boom-refueled and Canadian CF-18s are probe-and-drogue! Canada is replacing their CF-18s with F-35As, which are boom-refueled, and so they will have to scrap and replace their aerial refueling assets because they’ll be incompatible with their new fighters. A US Navy aircraft carrier working with Japanese F-15Js or a US Air Force unit teamed with French Rafales will have the same incompatibility.

The Missed Opportunity

Understandably, the US Air Force has not wanted to convert its fighter fleet to probe-and-drogue. It would mean that fighters escorting bombers - or even a mixed formation of older boom-refueled and (hypothetical) newer probe-and-drogue fighters - would need multiple refueling assets, or a tanker that can give for both. Notably, the KC-46 and A330 MRTT modern tankers do have both systems.

The opportunity is in the F-35. A single-seat, single-engine fighter, the F-35 was designed as a multi-service aircraft to replace several types in the US Air Force, US Navy, US Marine Corps, and the British Royal Navy. Three variants exist based on how they are expected to take off and land (runway, aircraft carrier, and STOVL), and because of their different customers, the F-35A (Air Force) is designed to receive fuel from a boom while the F-35B (Marines, Royal Navy) and F-35C (US Navy) have probe-and-drogue. The F-35A has space reserved in its nose for a refueling probe, but never had one fitted. In theory, an export customer could pay to develop that probe, but so far none has even though e.g. Canada has to replace its refueling tankers to support the F-35A.

But what if the F-35A could receive fuel from either system? Suddenly, a US Air Force squadron based in Guam or Japan could receive fuel from a US Navy tanker like the MQ-25. Those aircraft could participate in a strike that otherwise the Air Force might not have tankers for during a crisis as it frantically allocates them to bombers and transports. Australia or Singapore could contribute F-35s to a strike from their home bases while the US Navy provides mission tanking, multiplying the effective size of a carrier air group. An F-35A limping home would have that many more options to refuel rather than ditch and hope for recovery.

The Broader Opportunities

Combined with a standardized use of probe-and-drogue for strike fighters, more unconventional refueling assets can be brought into play.

"KV-22" Ospreys 

Tyler Rogoway writing for Jalopnik wrote of an intriguing scenario where a navy destroyer could carry an MV-22 with an aerial refueling kit (it's not clear to me if it was ever tested or entered service  [Update 6/10/2025:  nope!]) directly into the path of a long-range strike. The "KV-22" would provide mission tanking to ensure the strike aircraft went towards their targets with full fuel tanks without risking a long-range flight of a KC-46. The destroyer could probably provide air defense during the tanking operation!

"KB-2" Spirits

In general, aerial refueling works best close to the target because fighters can burn a huge amount of fuel in combat. Modern tankers are based on commercial aircraft and are high-priority targets, so they have to stay further away. The B-2 Spirit bomber is due for retirement as its replaced with the B-21 Raider, partly because its low-observability ("stealth") is no longer effective against the best sensors. But it's a big platform that's still very survivable; what about doing the same conversion on it as the KA-3B Skywarriors of the 1950s and putting a big fuel tank and hose-and-drogue in the bomb bay? Now you've got a tanker that can accompany stealth fighters and stealth bombers practically all the way to the target. Fitting a drogue would require fewer structural changes and be more compatible with stealth than a boom because it would be fully retractable and standalone kits already exist.

Conclusion

Like any project, getting all of the assets for an airstrike into the right place at the right time is difficult. It becomes easier the more options and alternatives are available to the planner. With a standardized aerial refueling option for the fighter fleet, planners have more optionality that go beyond KC-46s and allied aircraft for the Air Force (and Navy) and Navy-only refueling assets. Having a common fleet also improves the return on investment for developing unconventional refueling assets like the KV-22 or KB-2. Opposing force planners have to assume a greater variety of ranges and approaches that a US-and-allied strike might have when considering their defenses.

If you have any comments, please reach out to me at blog@saprobst.com or this page is cross-posted at LinkedIn and you can leave a comment there.