Why The Navy Needs A Really Large Tanker Aircraft

Once again, we are honored to have a timely guest post from Mr. Bustamante with his thoughts on Navy tanker aircraft needs.  Please be sure to read his bio at the end of the post.

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Why the Navy Needs a Really Large Tanker Aircraft

Some Unruly Thoughts on Strike Warfare Against a Peer Competitor [1]

Figure 1. S-3Bs Conduct Aerial Refueling with the Hose-and-Drogue System

Source: open source

If the U.S. Navy expects to employ carriers against peer competitor who can establish substantial Anti-Access and Area Denial (A2/AD) defenses, it will need large tankers, much longer ranged tactical aircraft, and long-ranged standoff weapons.  The Center for Strategic and Budgetary Assessments has published several excellent analyses papers making the case that we face adversaries with A2/AD defenses designed specifically to counter American naval and air-superiority extending from 1,000 nm, to1,500 nm or more from a hostile coast.[2]  It is important to note that ships, submarines, aircraft are not automatically destroyed when they enter into an area protected by a sophisticated A2/AD network, but they do risk detection and ultimately destruction that is directly related to the time exposed to the enemy maritime strike-reconnaissance network.  This presents a formidable range requirement for naval aircraft designs built in the last four decades and one that seems unlikely to be met satisfactorily with external fuel systems like conformal fuel tanks.[3]  Ironically, a typical 1960s carrier task force had both long ranged attack aircraft (A-3s, A-6s, and A-5s), and the tanker assets necessary to support escorting fighters for long range strike missions.[4]  The USN today, however, finds itself without long ranged aircraft due to decades of aircraft procurement policy favoring sortie generation over “deck load strike”, failure of the A-12 program, and retirement of long-ranged legacy aircraft.  The requirement for a long range attack aircraft and a big tanker is driven by the physics of fuel consumption and the relatively short range of carrier aviation.  Tanker aircraft allow strike packages to launch with maximum weapons load, but minimum fuel loads, then aerial refuel to maximize fuel load, while simultaneously reducing stress on airframes and extending the life of aircraft.  Large tankers are not only more efficient at delivering fuel, they are also a welcome savior for aircraft returning with combat damage, or Combat Air Patrol (CAP) aircraft returning from an extended mission.  While the F/A-18 is criticized for its relatively short combat radius, the reality is that the longest ranged carrier-based fighters would be challenged by today’s A2/AD defenses.[5]  The current solution to this dilemma is provided by U.S. Air Force, which operates the core of U.S. military aerial refueling fleet, largely consisting of ~460 KC-135 and KC-10 aircraft.[6]  These aircraft have performed yeoman service for naval aviation, but the USAF tanker fleet is prioritized for USAF requirements: delivery of large volumes of fuel to a single large bomber.  USAF tankers are primarily configured to use a unique “flying boom” fuel delivery system, a rigid, telescoping tube that the tanker aircraft extends and inserts into a receptacle on the aircraft being refueled; however, Navy and Marine Corps aircraft refuel using the “hose-and drogue” system, which is a flexible hose that trails from the tanker and drogue (windsock) that stabilizes it in flight.[7]  The USAF also uses JP-8 fuel, while the Navy uses JP-5.  In order to fuel USN and USMC aircraft, Air Force tankers generally have to flush their tanks and install a modified hose-and-drogue system, the inventory of which is sufficient to equip about a third of the tanker fleet.[8]  The new KC-46A is equipped with both the flying boom and the hose-and-drogue systems built into the airframe, but aircraft fuel compatibility remains an issue. 

Figure 2.  USAF KC-135A Refueling a B-52D¹

Source: open source

1.  The flying boom system designed specifically for fast, efficient refueling of very large aircraft like bombers.

The KC-46A is also just entering production and the current procurement plan is for only 179 aircraft.[9]  The balance of the USAF tanker fleet is also old and shrinking.[10]  Moreover, the USAF is likely to need every tanker to support a long-range bomber campaign in a high end conflict and these aircraft will be based to support USAF missions.  This is likely to leave Navy aviation without desperately needed aerial refueling capability in war.  This article will first examine the long range strike mission, review the aerial refueling requirements needed to support strike packages, and then show why current naval aircraft are not well suited the role.  Finally we will suggest some solutions to the issue.

Figure 3.  USAF KC-46A Refueling a Pair of F/A-18s¹

Source: open source

1.  The KC-46A has both the flying boom system; and the hose-and-drogue system.

We should ask ourselves, does the USN have a requirement to conduct long range strike operations using carrier based aviation?  Dollars are tight - a large tanker, and possibly a large tactical aircraft program, must fully justify the additional expense.  We could accept the status quo where long-ranged naval strike missions are tied to the availability of USAF tanker assets.  After all, the USN, and USMC used USAF tankers to support long missions to Afghanistan following 9/11.  Besides, the USAF is tasked with deep inland strikes; the USN has plenty of RGM/UGM-109 Tomahawk missiles for long-range strikes and highly capable submarines for clandestine launches.  Finally, there is the argument that carrier aviation exists to provide local air superiority for naval task forces – thus an alternate strategy for carrier employment might call for blockade, minelaying, and commerce raiding instead of deep strike.  In the end, none of these propositions are entirely acceptable; particularly given that the Navy had a plethora of tankers and long-range attack aircraft in the middle of the last century.  This is a problem with a readily definable technical solution that was worked out in the 1950s and then fielded.  Large organic tanker capability is incredibly useful, even when conducting strikes well within the range of strike aircraft.  USAF tankers are not always going to be conveniently based to support naval strikes, especially if the Navy pursues operations outside the USAF’s primary theater of operations.  In practice, USAF aircraft flying from known, geographically fixed bases may prove to be more vulnerable to attack than an aircraft carrier.  The submarine launched deep strike mission is in direct competition with the use of submarines for the critical anti-submarine warfare (ASW) mission and the commerce raiding missions, which I give much higher priority.  Further, an operational shift, or technological breakthrough favoring ASW might dramatically affect submarine survivability or effectiveness.  Finally, a good military policy is to retain redundancy and flexibility with weapon systems and units where possible. 

Modern tactical air operations place a premium on Suppression of Enemy Air Defenses (SEAD); the ratio of aircraft actually delivering steel on target might only be one out every three or four planes.  Most of the aircraft in a strike package will be fighter escorts, electronic warfare aircraft, SEAD aircraft, command and control aircraft, and other air frames, just to make sure the bomb droppers get to their weapon release points.[11]  During the Gulf War, strike packages of up to 50-60 tactical aircraft were generally required to assure the penetration of 12-16 aircraft with ground attack munitions!  The proliferation of advanced SAMs and advanced fighter aircraft gives us little hope that the situation will dramatically improve.  Additional considerations are the extensive fortifications constructed by many potential adversaries to protect key military and civil infrastructure to complicate U.S. strike operations.  This will demand larger ordinance loads, and also gives us little hope of using external fuel tanks extensively as a solution to extending aircraft range.

So what would it take to support the fuel needs of a carrier task force (TF) strike package of 60 or so aircraft?  I am assuming the TF is willing to risk a high speed dash at 30 knots to penetrate 240 nm into the A2/AD network (~8hrs), and that stand-off weapons range is 60+ nm, so the strike package needs to penetrate (fly) about 900 nm get to weapons release point for stand- off weapons   The key determinants are based upon the combat radius and fuel capacity of the aircraft flying in the strike.  Table 1 below gives us a quick summary of open source data in very rough approximation of the fuel and combat radius characteristics of selected naval aircraft.  Aside from the F/A-18E and F-35C, several historical aircraft are included as “place holders” to approximate potential performance of future aircraft. 

Table 1.  Fuel and Combat Radius Data for Tactical Naval Aircraft

Source: open source data is approximate and are for illustrative purposes.

1.  Combat radius is a very complex and qualified figure, see end note 2.

2.  F-35C figures are yet to be demonstrated.

The F-111 was included in the table because it was originally intended to be a joint USAF/USN carrier capable design and approaches the maximum size and weight of carrier capable airframes like the A-3D Skywarrior and A-5 Vigilante, arguably the closest aircraft to a strategic bomber that the USN has produced.[12]  The take away is that naval aviation, now based upon the F/A-18, is short ranged, and hugely dependent upon aerial tanking to conduct very long range strikes.  Even the “long-ranged” F-14 has qualifications.  A very rough estimate for an alpha strike package of 60 F/A-18 aircraft (to include F/A-18Gs) will require at least 36,750 lbs. of fuel, and three refueling operations per aircraft to reach 900 nm.  A strike package of 60 aircraft would require over 2.2 million lbs. of fuel!  This figure could overstate the actual fuel requirement because long-range missions may allow aircraft to operate at speed/altitude profiles that significantly enhance their fuel efficiency.  On the other hand, commonly quoted combat radii, do not address the inevitable delays that occur when aerially refueling dozens of tactical aircraft.  Also note, that this mission also requires tankers operate at least 600 nm from the carrier.  The situation improves slightly for an all F-35C strike package (27,990 lbs. per aircraft, 1.7 million lbs. of fuel for a 60 aircraft formation – but it still is a formidable requirement.  It is also questionable if the USN will buy a sufficient number of F-35s, and even if it does, the only tactical jammer currently in the U.S. inventory is the F/A-18G.  The F-35 is supposed to deliver many capabilities that promise to reduce the size of strike packages and increase survivability, but these have yet to be demonstrated.  A partial solution is of course to use external fuel tanks, but these come at a performance penalty and also increase the detectability of the strike force.  For these reasons, and to simplify what can be a very complicated analysis, the strike package fuel requirement assumes internal fuel loads only.

Having stated the requirement, what tanker assets are available to support the strike tanking requirements?  Table 2 below provides a summary of selected aerial refueling aircraft in the U.S. arsenal and matches them to the number of tankers required to deliver 1.7 million pounds of fuel to support a 60 aircraft strike.

Table 2.  Summary of Selected U.S. Aerial Refueling Assets

Source: open source data; approximations are for illustrative purposes.

1. Note that with the exception of the KC-135, all of the other aircraft options fail to provide fuel at useful ranges.
2. Figures are rounded up to the nearest whole number of aircraft.
3. The more common EKA-3B could deliver 21,000 lbs. of fuel at 460 nm, enough to fuel 2.2 full F-4Js, but it also retained significant stand-off jamming capabilities and could still carry ordinance while operating as a tanker.  The KA-3 and EKA-3B were far and away the best aerial refueling assets the Navy built.  They were also the largest carrier capable aircraft ever built with about 82,000 pounds maximum take-off weight.
4. With two 300 gallon tanks.
5. The KS-3A program was cancelled afte a single prototype was built.  Had it entered production,it arguably might have been the most capable dedicated Navy tanker.
6. The F/A-18E configured as a "buddy tanker".

What Table 2 really demonstrates is the huge load efficiency of very large, land-based tankers with maximum take-off weights exceeding 320,000 lbs. (the KC-46A has a maximum take-off weight of 415,000 pounds - over five times heavier than the largest carrier aircraft ever deployed, the KA-3).  This analysis also underestimates the tanking requirements of a long range strike package because with the exception of the KC-135, all of the other aircraft options fail the ability to provide fuel at useful range.  It also shows that the best tanker the Navy ever acquired, the KA-3, was still inefficient as a tanker, requiring an almost one to one ratio of tankers to F-35Cs to support a 900 nm strike.  The very worst tanker option is the F/A-18E operating as a “buddy tanker” due to the short intrinsic short range of the airframe.  In fact, the F/A-18E “buddy tanker” configuration will burn most of its transfer fuel capacity to reach 600 nm. 

Figure 4.  The Navy’s Best Tanker Ever - an EKA-3B Skywarrior Refuels an F-14

Source: A-3 Skywarrior Association

This is reminiscent of the U.S. Army Air Corps fiasco in WWII called Operation Matterhorn: an ill-conceived strategic bombing campaign against Japan by basing B-29s bombers in India and staging them from airfields in China.  Every gallon of fuel, every pound of ammunition and other military supplies had to be flown over the Himalayas to China.  Because the B-29 was inefficient as a tanker, it took seven round trip B-29 flights to build up enough fuel for a single B -29 mission against Japan; prompting General Curtis E. LeMay the commander of XX bomber Command to say: “The scheme of operations had been dreamed up like something out of ‘The Wizard of Oz,’ ...”[13]  Carrier aviation, lacking both a large tanker, and long ranged aircraft, is in danger of repeating this error.

Matching requirements to assets, suggests a number of options the U.S. Navy can, and should take to improve its strike capacity against first class adversaries with advanced A2/AD defenses.  Specifically:

1)     In the short term, the Navy should study the feasibility of returning some of the 100 A-6E aircraft in storage to service after refurbishment and conversion into KA-6Es.  The A-6E was given new composite wings shortly before retirement and could provide a great deal of relief to the air wings.  Conversion to unmanned or optionally manned operation should be considered.

2)     Long term, the Navy needs to procure a very large, carrier capable tanker aircraft with a maximum take-off weight of 80,000 pounds or larger, and an objective transfer fuel load of 40,000 lbs. delivered to 600 nm.  This aircraft should follow the “payload over platforms” design philosophy and provide a robust “pick-up truck” functionality over stealth and other features.

a)     The aircraft could be unmanned or optionally manned.

b)     A flying wing or blended wing design seems appropriate to maximize lift and internal fuel capacity.

c)      The tanker should have several "joint" features for maximum compatibility with the USAF and allies that use the flying boom (e.g.  Australia):

i)        Incorporate a flying boom receptacle to enable the new tanker to receive fuel very quickly from USAF tankers, while simultaneously refueling USN aircraft.[14]  This would open a number of tactical advantages, shorten refueling times, and allow strategic tanker aircraft to complete their missions more rapidly.

ii)      Incorporate certain USAF mounts for large capacity external fuel tanks. 

iii)    Possibly incorporate a flying boom for refueling USAF fighters.

3)     From a joint perspective, the Navy and Air Force must continue to integrate operations and ensure equipment interoperability. 

a)     The U.S. military needs to move to a single aviation fuel type to minimize logistics issues.  Given the number of aircraft in each service, this means that the Navy and Marine Corps should adapt JP-8, which is similar in chemical composition, but has a lower flashpoint than JP-5.

b)     The Navy must also seriously consider incorporating the USAF flying boom/receptacle compatible system into large aircraft like the P-8 or future attack aircraft.  It also means that the USAF must maintain sufficient numbers of Wing Air Refueling Pods for legacy tankers to support naval aircraft.  This is key, the Navy must support the USAF 100% in obtaining funding for these pods.

4)     Future naval aircraft must place a much higher emphasis on range and payload than the past three decades.  Plainly stated, this requirement greatly favors a large, long-ranged heavy attack aircraft; the same physics of moving large bomb loads over great distance was exactly what drove the procurement of the A-3, the A-6, and the A-5.  This aircraft will need to be larger than the X-47B - it could also be a drone or optionally manned.  It should incorporate certain USAF mounts for large stand-off weapons and large capacity external fuel tanks. 

5)     Improve stand-off ranges with a very long ranged (1,200 to 1,500 nm) air to ground weapon.  This also favors a large heavy attack aircraft in A-3/A-5/F-111weight class. Consider:

a)     Adapting Navy aircraft to carry long ranged USAF air-to-ground cruise missiles with conventional warheads to support strike operations.  This implies a large attack aircraft to carry them: for example an AGM-129A missile weighs over 3,500 pounds.[15]

b)     Procure a long ranged air-to-ground ballistic missile with a conventional warhead to support strike operations.[16]

These are appropriate actions for naval aviation but the Navy in general needs additional reforms to conduct strike warfare against modern a2/AD defenses.  First and foremost is the procurement of a very long ranged (1,200 to 1,500 nm) ship launched cruise missile and/or ballistic missiles for strike operations.  These weapons need not only greater range than BGM-109 tomahawk, they require more sophisticated warheads, for example anti-radiation seeker heads, earth penetrating warheads, and EW packages like jammers.  Serious consideration to stealth and hyper velocity propulsion is essential. 

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[1] This article addresses high end war against a peer competitor, not COIN operations.

[2] See AirSea Battle: A Point-of-Departure Operational Concept, May 18, 2010 by Jan van Tol, Mark Gunzinger, and Andrew F.  Krepinevich and Jim Thomas.  Available at  http://csbaonline.org/wp-content/uploads/2010/05/2010.05.18-AirSea-Battle.pdf

[3] The details of combat radius are highly technical and dependent upon a number of factors (ordinance and fuel loads, ingress and egress altitude, dash speed, weapon drag, etc.), but typical tactical aircraft combat radii range from 350 nm to about 600 nm.  External fuel systems work well, but impose trade-offs in performance, particularly in maneuverability, radar cross section, and use, or interfere with, munition hard points. 

[4] This capability was developed because Admirals Mitscher and Sallada proposed a nuclear bomb capable attack bomber in 1945 with a 1,000 nm combat radius leading directly to the A-3 Skywarrior and later the A-5 Vigilante.  U.S. Aircraft Carriers, An Illustrated Design History, by Dr. Norman Friedman, 1983, pages 240 and 241.

[5] The F/A-18 does what it was designed to do, the problem is the carrier air wing lost the supporting cast of aircraft types.

[6] Formal Joint air refueling operations between the Air Force and Navy started in the early 1970s.  A 1988 memorandum of understanding (MOU) established joint air -refueling concepts.

[7] Congressional Research Service report RL32910,  Air Force Aerial Refueling Methods:

Flying Boom versus Hose-and-Drogue, by Christopher Bolkcom pages 2 and 3, June 5, 2006.

[8] The KC-10 is configured to allow the alternate simultaneous use of either the flying boom or the hose and drogue if equipped with Wing Air Refueling Pods (WARP).  This does not solve the issue of the services using different fuel types.  Only about one out of every three USAF KC-10s had Wing Air Refueling Pods (WARP), and these are low priority procurement items for the USAF.  Naval Air Refueling Needs Deferred in Air Force Tanker Plan by Hunter C. Keeter, Sea Power magazine, April 2004.

[9]http://www.af.mil/AboutUs/FactSheets/Display/tabid/224/Article/104537/kc-46a-tanker.aspx

[10] GAO found that the average age of the KC-135 fleet was 35 years back in 2003.  GAO-03-938T, page 4.

[11] A combat grouping of aircraft with different capabilities that are launched together to perform a single attack mission

[12] The C-130 is the largest aircraft to land and take off from aircraft carriers.  In October and November 1963, a KC-130F (BuNo 149798) made 21 landings and take-offs on the USS Forrestal.  It is important to note that the C-130 essentially shut down normal flight deck operations and was (remains) unsuitable for normal carrier operations.

[13] The Matterhorn Missions, by John Correll, pages 62-65, AIR FORCE Magazine, March 2009.  http://www.airforcemag.com/MagazineArchive/Documents/2009/March%202009/0309matterhorn.pdf

[14] Designed properly, a USN tanker could receive fuel from a USAF tanker via the boom, while also fueling two Navy aircraft.  In the case of a KC-10, or KC-46A, the possibility of fueling the Navy tanker (via the flying boom) and four tactical aircraft via hose and reel (two from the USN tanker, and two from the USAF tanker, is a possibility.

[15] http://www.af.mil/AboutUs/FactSheets/Display/tabid/224/Article/104543/agm-129a-advanced-cruise-missile.aspx

[16] The Douglas AGM-48 Skybolt Air-Launched Ballistic Missile from the 1950s suggests one possible weapon. It was very heavy weighing almost 11,000 pounds.

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Mr. Bustamante is a retired naval officer who served the majority of his career as a Naval Special Warfare Officer, but also as a Surface Warfare Officer and Foreign Area Officer.  He is a graduate of the U.S. Naval Academy with a degree in Systems Engineering.  He also holds a Master of Science degree in Defense Analysis (Operations Research) from the Naval Postgraduate School in Monterey, California. After retiring from the Navy, Mr. Bustamante worked for the legislative branch as an auditor and analyst, as a civil servant with the United States Department of State, and also in the private sector as an analyst in information technology project management.

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