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There are two main types of aerial refueling, the boom and the drogue. The US uses both, while most other countries use just the drogue.

How are they different and why does the US use both?

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    $\begingroup$ Fun fact, the first air to air refueling was done when a wing walker with a 5gallon jerry can strapped to his back stepped from one biplane to another. $\endgroup$ – Max Power Jul 20 '18 at 23:32
  • $\begingroup$ related aviation.stackexchange.com/questions/51692/… $\endgroup$ – Pilothead Oct 31 '18 at 11:02
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The flying boom method uses a rigid boom which is "flown" by an operator in coordination with the pilot in order to make a connection with a receptacle on the second aircraft. The boom is retracted when not in use. Though it can do damage if it comes in contact with an aircraft, the operator can quickly move the boom if needed.

Refueling with boom

The probe and drogue method uses a trailing hose with a basket on the end. Pilots will guide a probe on their aircraft into the basket to connect with the hose. The hoses are retracted when not in use. Though the crew has less control of the drogue, which can still cause damage, there is less danger to the aircraft than from a boom, and it could allow the aircraft to stay further away from the tanker.

Refueling with drogue

The boom method was developed early on in the Cold War, when Strategic Air Command had many large bombers that needed to be refueled. They needed a method that would transfer fuel as fast as possible in order to reduce the time it took to transfer the large amounts of fuel needed. Because the boom is rigid, it is capable of a higher transfer rate. The importance of bombers meant that SAC got their way, and the KC-135 fleet was equipped with booms. Today, almost all US Air Force planes capable of aerial refueling use the boom system.

The US Navy on the other hand, along with most aircraft in other countries, uses the drogue system. Though this method is not capable of the high transfer rates of a boom, it is much more flexible. A refueling aircraft may only be fitted with one boom, and this requires extra design work and integration with the fuselage. The drogue system, on the other hand, is more simple, and does not need a dedicated operator. This means that it can be more easily fitted to the refueling aircraft, even other fighter planes, and larger aircraft can have multiple drogues.

Another point is that smaller aircraft such as fighters are not capable of receiving fuel at the full rate the boom provides, so they have less benefit from the system. Although a boom can have a drogue adapter attached, this still commits the tanker to one aircraft at a time and one type of system per flight. Also, aircraft such as helicopters cannot use a boom system.

When the Air Force was looking at a replacement for its tanker fleet in the early 2000s, a study was done to determine what standard the new tanker should support.

The report suggests some options for the best combination of methods. In the end, the Air Force selected the KC-46 for the contract, which will include both the boom and the drogue options for refueling. This will provide better support to aircraft from other branches or countries, while maintaining support of the existing aircraft that use a boom.

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    $\begingroup$ The basket can actually do tons of damage. Its very heavy and made of steel. Even a glancing blow has been known to do 10's of thousands of dollars worth of damage. Basket strikes are almost always a class charlie mishap. Oh yes, and you should add a blurb in there about the Navy having much more competent pilots. Other than that, spot on. $\endgroup$ – Rhino Driver Apr 10 '15 at 19:00
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    $\begingroup$ @RhinoDriver thanks for the info, always good to have a first hand account. I will incorporate that. $\endgroup$ – fooot♦ Apr 10 '15 at 19:08
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    $\begingroup$ Another reason the Navy kept the hose and drogue system is interoperability with foreign forces, most of which still use it. And of course KC-10s (and I think the -135 as well) can be fitted with underwing pods to refuel using probe and drogue. $\endgroup$ – jwenting Apr 11 '15 at 18:19
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    $\begingroup$ @jwenting Some -135s can be fitted with pods; it also supports a metallic drogue adapter on the end of the boom (which according to Wiki is even more of a pain to deal with than a regular drogue). The -10 doesn't even need underwing pods (although some can take them); it has a roughly-centerline hose-and-drogue built in. As for foreign forces, while foreign-built aircraft all use probe-and-drogue, foreign forces with USAF-targeted planes (e.g. F-15, F-16) need to use booms to refuel them. $\endgroup$ – cpast Apr 12 '15 at 4:46
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    $\begingroup$ @RhinoDriver I have a sneaking suspicion that last part of your comment may be a tad biased. ;) $\endgroup$ – T.J.L. Jan 2 '18 at 21:39
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The US Air Force and the US Navy have a very different history, so they approach things quite differently and feel their respective way of doing things is superior.

The US Air Force started as the Aeronautical Divison of the US Signal Corps and later became the US Army Air Forces (USAAF), and it inherited the traditions from the Army: Discipline and strict adherence to procedures, basically what was started when Baron von Steuben trained the first American soldiers.

The Navy used to give their commanders much more freedom: When away on a ship, the captain had to decide for himself what the best tactics would be. This can still be found in the Navy's flying forces today: Pilots are much more encouraged to think for themselves instead of following detailed procedures.

Therefore, both will instinctively reject what the other prefers: When the Air Force selected the F-16, the Navy had to prefer the F-18. And so on.

For aerial refuelling, it makes indeed more sense to use the boom technique when large amounts of fuel need to be transferred to big bombers. If you need to top up fuel for a number of smaller aircraft, however, the drogue-and-chute system is the better choice. The mutual competition between the Forces has only helped to cement this diversity.

The advantages of the boom over the drogue technique are:

  • much higher transfer rate. This is the reason the boom method was developed to transfer lots of fuel to SAC (Strategic Air Command) bombers. Other nations' bombers and large aircraft prefer the probe and drogue method.

  • Maneuvering is done by the boom operator. While the drogue method requires the recipient to manoeuver his aircraft's probe into the center of the drogue, the boom method requires the recipient only to fly in formation with the tanker while the boom operator does the rest.

  • There are fewer boom operators than pilots, so the boom operator is likely to be more experienced in the refuelling process.

The disadvantages are:

  • The tanker needs to be a big aircraft which can afford to include a boom operator compartment. There is no possibility for buddy-buddy refuelling (except between two tankers).

Also most aircraft, including many of the USAF, can not accept fuel at the rate that a boom can provide, so much of the extra capability goes unused.

  • Retrofitting existing aircraft for boom refueling is much more complex than mounting a fuel tank with a hose and drogue at its end to an aircraft. Unless the aircraft in question is a large aircraft, the retrofit to boom is virtually impossible.
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    $\begingroup$ the navy investigated the F-16 seriously, came (IMO correctly) to the conclusion that the required modifications would leave it too heavy, too slow, incapable of performing its mission. So they went with the F/A-18 instead, which was based on the YF-17 that lost the USAF competition and proved to be better suited for turning into a carrier aircraft. $\endgroup$ – jwenting Apr 11 '15 at 18:21
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    $\begingroup$ @jwenting: I remember the discussion well: The Navy reasoned that the F-18 must be more capable, because hanging it full of ordnance would affect performance less that doing the same with the F-16. Yeah, right. (This only shows that the F-16 has cleaner aerodynamics). The same cherry-picking of arguments went on with the number of engines. $\endgroup$ – Peter Kämpf Apr 12 '15 at 11:35
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    $\begingroup$ 2 engines for an aircraft spending a lot of time over the sea is a good idea. As was shown even during flight testing of the YF-18A when a fan blade cracked, causing one engine to have to be shut down. The aircraft returned to base safely, a YF-16 would have crashed. AFAIK main concern with the F-16 for the navy apart from the engines was the amount of work needed to make it carrier capable, and the penalty to the performance that would cause. $\endgroup$ – jwenting Apr 12 '15 at 18:51
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    $\begingroup$ Indeed, the F-18 E/F/G are the best carrier aircraft the Navy has ever flown. Several design features make it incredibly reliable in the carrier environment, and I would definitely place it well above a modified viper for this flight environment. The engines are incredible, throttle response at the boat is the best its ever been in a carrier aircraft, the flight controls are phenomenal (especially low speed control) and it can carry a larger payload, has better radar, is more upgradable--the list goes on. The viper is great at what it does, but not for carrier ops. $\endgroup$ – Rhino Driver Apr 13 '15 at 2:37
  • $\begingroup$ Outstanding information provided here. However, I doubt the attitudes of our Army and Navy towards each other are "instinctive", even during mating season. But what can be gathered is that, with advances in technology, better control of the drouge may be possible. Naturally, the flying boom reflects Air Force philosophy, smaller/automated versions (even putting simple stabilizer fins on the drouge) may be yet seen in the Navy. $\endgroup$ – Robert DiGiovanni Oct 31 '18 at 1:07
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The Navy carriers also need to be self sufficient and so need to be able to launch their own tankers from their deck. Boom tankers are too large for this so the Navy relies on the buddy buddy system where one F-18 is the tanker and trails a hose for his buddy to refuel from.

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The chief reason for this was fuel transfer rate vs flexibility for tactical aircraft. The flying boom, as pointed out by others here offers a faster fuel transfer rate and makes it more suitable for strategic operations ie refueling large bombers en route to their targets, as the USAF had largely utilized their tankers for. That being said flying booms require a specialized aircraft for that role whereas probe and drogue system can be employed much more flexibly on a wide range of airframes. The Navy and other NATO nations found this more convenient as a means to provide gas for tactical aircraft during operations as fighters are an almost universal Air Force commonidy and many nations were not equipped with dedicated tankers and strategic nuclear bombers. The Navy liked the probe and drogue system as well due to the limited space available on carriers for a fleet of tanker aircraft and it is more convenient for an exiting fighter or attack aircraft to use “buddy stores” - external tanks and a hose and reel pod to provide extra gas for the air wing. Cold War tactical operations, Operation Desert Storm and joint military operations in the years since then have made the USAF adapt its tanker fleet to accommodate both types of refueling systems. KC-135, KC-10 and the new KC-46 aircraft are equipped with both the flying boom as well and the probe and drogue refueling systems now.

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