Commander William Earl Fannin, Class of 1945, Captsone Essay Contestenerational transformation in the nature of combat. The U.S. Navy is no exception. Just as jet-engine technology redefined air combat during World War II and the Cold War, 21st-century advanced weapon systems continue to reshape the tactical theater. As illustrated by the Navy’s recently published Cooperative Strategy for 21st Century Seapower, the present-day warfighter faces a broad range of issues, including adversaries’ increased anti-access/area-denial (A2/AD) capabilities, exploitation of cyberspace and the electromagnetic spectrum, and long-range ballistic-missile technology.
At the forefront of these rising capabilities is in the Indo-Asia-Pacific. As a result, the Cooperative Strategy for 21st Century Seapower estimates that 60 percent of all Navy ships and aircraft will be based there by 2020. Not surprisingly, the strategic shift to the Pacific has inspired nations such as China and Russia to accelerate development and testing of weapon systems designed to prevent our access to this region. China boasts a variety of antiship ballistic and cruise missiles with ranges far exceeding the operational reach of our carrier strike groups (CSGs). As far as air superiority, the soon-to-be-operational Chengdu J-20 is the culmination of the latest in Chinese supercruise capabilities, maneuverability, and stealth technologies and currently the top contender against the U.S. F-22 Raptors and F-35 Lightning II fighters.
Present technologies being employed to face the challenges of the Indo-Asia-Pacific region are the coveted fifth-generation fighters and stealth bombers. The exact characteristics of these fighters are still debated but common among them are all-aspect stealth, advanced avionics suites, and highly integrated computer systems designed to network various platforms within the battlespace.
Stealth . . . and its Constraints
The current defining aircraft among the fifth-generation platforms is the F-35. Capable of seamlessly fusing information from a variety of on-board sensors, the F-35 provides unmatched situational awareness in a tactical environment. Armed with both kinetic and electronic-warfare weapon systems, the F-35 is the most capable platform to operate in a denied theater. Challenging the air superiority offered by the F-35, however, is the aforementioned Chinese J-20, which is expected to be operational as early as 2017. Suspiciously similar to the U.S. F-22, the J-20 was designed specifically for counter-stealth capability and poses a considerable threat to any potential maritime strike package.
Though not necessarily relevant to naval application, strategic stealth bombers are another key player in the A2/AD dilemma. The U.S. Air Force’s current heavy-penetration strategic bomber of choice is the B-2 Spirit. Capable of deploying both conventional and thermonuclear warheads, the B-2 offers considerable weapons delivery as well as range and stealth. However, in the context of an A2/AD scheme, the B-2 falls short with regard to speed and ability to integrate with a CSG. In addition, China’s growing counter-stealth capabilities continue to reduce the margin of detection and the B-2’s lack of maneuverability and air-to-air missiles leave it defenseless should it be detected and engaged.1
The issue presented by China’s A2/AD strategy is the U.S. Navy’s inability to maintain “all-domain” access in the Western Pacific. Given the geographical challenges presented by the Pacific, the Navy is forced to operate forward and rely on the networked capabilities of the CSG. Integrated computer systems, offered by the F-35, enhance situational awareness and command-and-control but are not robust enough against China’s advanced electronic attack capabilities. Stealth, offered by both the F-35 and the B-2, places constraints on speed and maneuverability and is becoming increasingly obsolete. Intercontinental ballistic missiles offer tremendous range but are stalemated by the political ramifications of nuclear war and slow responsiveness.2
To ensure success in the Indo-Asia-Pacific region and keep China in check, the Navy needs to recognize the diminishing strategic advantage of fifth-generation fighters and stealth-bomber technology and take a broad and imaginative approach to resecuring “all-domain” access for not just the years to come but for the sixth-generation battlespace that lies ahead. With immediate and uncontested delivery of weapons being the goal, the issue seems to boil down to one dominating factor: speed. With fifth-generation fighters currently capable of obtaining speeds marginally above Mach 2, the Navy needs to think faster, much faster.
‘Bridging the Power Gap’
Traditionally, “hypersonic” refers to speeds in excess of Mach 5, or five times the speed of sound. Depending on the altitude of operation, this would equate to nearly 4,000 miles per hour, which, historically speaking, is possible. In fact, the current world record holder for the highest speed recorded in a manned powered aircraft was the North American X-51, which rocketed to Mach 6.7 back in the early ’60s. Although the distinction between supersonic and hypersonic speeds is often blurred, several peculiarities in hypersonic flow warrant separate discussion.
Most jet aircraft and weapon systems employ turbojet engines, which use an assembly of blades to compress and then ignite air to provide thrust. However, the designs of most air-breathing jet engines max out near Mach 2, where the assembly of blades can no longer reduce the incoming air to the subsonic speeds required for combustion.
In order to reach Mach 5 with an air-breathing engine, combustion will need to occur in a stream of supersonic air. One design method used to achieve such performance is a supersonic-ramjet (scramjet) engine. A ramjet is a form of air-breathing engine with no moving parts that uses forward motion, rather than a rotary compressor, to compress incoming air for combustion. A scramjet is simply a ramjet that ignites the air-fuel mixture without slowing the incoming air to subsonic speeds. Injecting and igniting fuel in supersonic flow poses a difficult engineering problem as it is akin to “lighting a match in a hurricane and keeping it lit.”3
Currently, the two most successful attempts to creating a functional scramjet system are NASA’s X-43A and X-51A Waverider. Deployed from carrier planes and then accelerated by a rocket booster, these experimental vehicles have proven the viability of scramjet technology. Launched in November 2004, the X-43A reached a record speed of Mach 9.68 and was the first fully controlled scramjet vehicle. Fast forward to 1 May 2013, the X-51A maintained a speed of Mach 5.1 for four minutes, the longest scramjet flight time on record.4
The issue with ramjet-scramjet engine technology is they cannot produce thrust at zero airspeed and therefore require assisted acceleration in order to begin combustion. Therein lies the present aerodynamic dilemma of “bridging the power gap.”5 Opponents of hypersonic development contend that such speeds cannot be achieved without employing rocket engines that require their own oxidizing sources, which adds tremendous amounts of weight, not suitable in a tactical environment. In order to be a viable investment, hypersonic propulsion would need the best of both air-breathing and rocket technology.
One proposed solution and cutting-edge technology, currently being developed by U.K.-based Reaction Engines, is the Synergetic Air-Breathing Rocket Engine (SABRE). Employing clever heat-exchanger technology, the SABRE is designed to provide propulsion from a complete standstill and accelerate all the way to orbital speeds. Originally intended as the primary propulsion system for a Shuttle replacement vehicle or even commercial flight, the SABRE could certainly find usefulness in a military application.
Future Naval Applications
Hypersonic technology can benefit both aircraft and weapon systems by providing rapid weapons delivery and virtually zero probability of being intercepted. Application of hypersonic technology in a naval context falls under two categories: long-range precision strike weapons or hypersonic capable “sixth-generation” fighters. The former shows the most promise with the recent success of the X-51A serving as a platform for future air-launched hypersonic weapon systems such as the U.S. Air Force’s High Speed Strike Weapon (HSSW) initiative.6 The Air Force estimates that the technology present in the X-51A can be applied to an HSSW by 2020 and be ready to enter service by the mid-’20s. As far as integrating with a CSG scheme, the HSSW is being designed to mount externally to an F-35, which would enable immediate and uncontested precision-strike capability.
The second approach to hypersonic application is the development of sixth-generation fighters. A far more forward-looking approach, sixth-generation fighters are meant to address the battlespace issues of 2030 and beyond such as advanced electronic attack, sophisticated air defense systems, and fully developed A2/AD theaters. In such a scenario, fighters would need to be able to independently operate deep within denied regions without the benefit of CSG support. Hypersonic capability would allow fighters to penetrate enemy defenses without being flagged by advanced early-warning systems and close-in sufficiently to allow for release of conventional subsonic-supersonic weapon systems. SABRE propulsion systems would be strong contenders in providing such hypersonic capabilities by allowing acceleration from standstill on the carrier deck to Mach 5 over denied waters.
History has shown that the success of any military campaign depends on a country’s ability to operate freely and unrestricted in the air and on land and sea. The U.S. Navy has frequently enjoyed this luxury and is therefore unaccustomed and, as it would seem, unprepared for a denied theater such as the one presented by China. Though regarded as a strategic and economic partner, China’s sphere of influence cannot be left unchallenged, especially given its recent extensive territorial claims and contention with the sovereignty of Taiwan, a long-standing U.S. ally in this theater. With the recent success of hypersonic technologies such as the X-51A and developing technologies such as the SABRE propulsion system, the U.S. Navy would be wise to consider further developing these technologies in preparation for the future battlespace. Although far from reality, preparing for the sixth generation of war is extremely necessary, especially given the uncontested advances in our adversary’s capabilities.
2. A Cooperative Strategy for 21st Century Seapower: Forward, Engaged, Ready (Washington, DC: Department of the Navy, 2015), www.navy.mil/local/maritime/.
3. “Ramjet/Scramjet Thrust,” National Aeronautics and Space Administration, www.grc.nasa.gov/www/k-12/airplane/ramth.html.
4. Mike Wall, “Air Force’s X-51A Hypersonic Scramjet Makes Record-Breaking Final Flight,” Space.com, 3 May 2013, www.space.com/20967-air-force-x-51a-hypersonic-scramjet.html.
5. Guy Norris, “Air-breathing Sabre Concept Gains Credibility,” Aviation Week, 30 July 2015, http://aviationweek.com/technology/air-breathing-sabre-concept-gains-credibility.
6. Guy Norris, “High-Speed Strike Weapon to Build on X-51 Flight,” Aviation Week, 20 May 2013, http://aviationweek.com/awin/high-speed-strike-weapon-build-x-51-flight.