Reeds Vol 14: Stealth Warship Technology

14 REEDS MARINE ENGINEERING AND TECHNOLOGY

STEALTH WARSHIP TECHNOLOGY

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CONTENTS ACKNOWLEDGEMENTS INTRODUCTION

IX X

1 RADAR Early Radar Stealth SR-71 Measuring Stealth Maximum Detection Range (MDR) and Radar Cross Section Stealth Approaches

1 6 8 11 13 19

2 VISIBILITY Dazzle Camouflage and the First World War Origins of Camouflage

30 30 36

3 INVISIBLE FUTURES Radar Metamaterials Optical Metamaterials

52 54 59

4 INFRARED Infra-red Heat Reduction IRCS Contributors The Laws of Infra-red Emission

66 66 71 78

5 MAGNETIC SIGNATURE Magnetic Stealth Degaussing Ships’ Hulls

82 82 86

6 THE ACOUSTIC THREAT AND OTHER SIGNATURES Acoustic Noise Various Environmental Factors Active Sonar Passive Sonar Sonar Comparison Cavitation Future Acoustic Technology Bioluminescence Wake Effects Extremely Low-Frequency (ELF) Signature Likely Future Cross Sections Biologically Inspired Design Emissions Control Policy

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95 95 97 98 99 100 102 103 104 105 108 108 109 111

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viii • Contents 7 MODERN STEALTH SHIPS Sweden United Kingdom Italian and French Destroyer Variants United States of America India Russia France Saudi Arabia Singapore Germany China

114 114 119 128 130 132 133 134 136 136 137 138

8 FUTURE NAVAL STEALTH PLATFORMS Queen Elizabeth-Class Aircraft Carrier A Brief History of the Build So Far Radar and Weapons Systems Embarked Fleet Air Arm? Carrier Construction HMS Queen Elizabeth (R08) UK FSC or Type 26 Frigate Weapons and Systems Modular and Flexible United States of America

141 142 144 146 146 147 148 149 151 151 152

SUMMARY

158

APPENDIX: KEY SHIP FACTS

160

GLOSSARY

167

ANSWERS TO NUMERICAL QUESTIONS

169

IMAGE SOURCES

170

INDEX

171

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ACKNOWLEDGEMENTS I would like to thank the following: Mr John Mc Crae for permission to use Type 45 Destroyer HMS Daring images at various construction stages; Mr Andrew Valente, Combat Index Webmaster, LLC, Naples, Florida, USA for archive imagery access; and Mr Kjell Göthe, of Kockums Sweden, for Visby stealth corvette pictures and extensive material about the class. I would also like to thank the meticulous manuscript checking and copy editing provided by the editorial services team at MPS Limited, Chennai.

I appreciate the BBC Radio 4 ‘Material World’ team for letting me loose to talk live about stealth concepts before disappearing ‘on air’ (24th April 2008), which first set me on the path to this book, and the Institute of Physics and the Institute of Materials which both published early crafting of ‘stealth’ ideas in 2008 and 2009.

I would like to thank my family motivators and in turn encourage them: Helena for her work with the disadvantaged of Mexico City, Sam for achieving Ten Tors Gold and teaching in Tanzania, Sara-Kate for her warmth, and care in Guides, Matt for his application of talents and introducing me to football and Ben for his love of learning and stories. I thank them for the few hours of reality each day! Your values and passions add meaning to my life. I thank my parents for motivating me in the past, believing I could learn to read even when my teachers said I wouldn’t! Finally, I especially thank Anne, my wife, for her patience and encouragement; you are the true love of my life.

To all and one I thank you.

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INTRODUCTION The missile navigating by inertial guidance approached with swift self-assurance the end of its 200 nautical mile pre-programmed journey, and after rapid target confirmation with its passive thermal imager reaches its objective to devastating effect. The target, oblivious of its peril, until the final moment of impact, could do nothing to counter this fatal blow.

Christopher Lavers

The scenario outlined above is not fiction; it is the real high-technology cutting edge of naval warfare today. For this reason, surface warships incorporated with stealth technologies take an increasingly vital role to ensure platform survival. Stealth’s principal aim is to make naval ships ‘invisible’ to an array of increasingly smart detection systems such as sonar and radar, combining ways that lower a platform’s emissions and those which eliminate reflected radiation, thus reducing detection range and threat vulnerability. This book seeks to communicate the latest interesting developments in stealth technology to a wider audience and to explore the paradigm shift ‘stealth’ represents in terms of warship design. It will focus on the transformational change in naval architecture, which is simplistically represented in the shape of modern warships, and dwells less on just providing lots of information or technical detail. Stealth Warship Technology will also discuss in a little detail something of the history of this subject.

In this book, I will provide an opportunity to develop a better understanding of the specialist practical issues and skills required in this naval sector. Some opportunity for basic numerical analysis and problem-solving are included at the end of each chapter for the more mathematical reader. However, the book is designed for those with a limited mathematical background in mind; it is my objective to communicate the fundamental principles of the subject to the many and not to provide tricky maths problems to solve for the few.

I will discuss several ongoing themes or issues throughout the book: surveillance, signature and cross section reduction as well as certain aspects of electronic warfare (EW). Surveillance entails an examination of both radar and infra-red non-imaging target detection systems as well as the latest visual and thermal imaging systems. The developments in high-resolution radar imaging cannot be underestimated in their significance at the beginning of the twenty-first century to future platform survivability.

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Introduction • xi Signature and cross section reduction consideration will investigate the various applied techniques that have been utilised to date and those which are likely to be employed to make ship targets less visible to current (and future) generations of surveillance systems. The topic of EW elicits a double-edged response from the informed reader.

EW involves the role of largely passive electronic support measures (ESM), the ‘listening’ devices which need to be coordinated with further electronic countermeasures (ECM) (various active and passive techniques available), and is both our best friend and, being also used by an equally surveillant enemy, perhaps our greatest foe.

The aim of this book is to ‘uncover’ the unto now ‘secret’ area of stealth warship design and the broader aspects of stealth technology using available public material and to stress the importance of materials used in the warship’s construction with information that already exists in the public domain, and how this influences all of a modern naval platform’s design parameters. Paradoxically, all the basic stealth concepts are easily accessible on the Internet, with a variety of stealth-related companies discussing their products in some detail. To a physicist or engineer who knows what they are looking for, even YouTube videos can now provide significant intelligence on both systems and their capabilities and mode of operation, saying nothing of the ability of modern mobile phones to provide a wealth of additional information and influence, as seen in the Arab Spring of 2011. A working title for this book was initially ‘Electromagnetic threats to warships’, but this not only fails to grasp the full extent of warship threats which encompass the traditional role of radar and visual detection, as well as nightvision devices and thermal imaging capability, but also does not address the acoustic underwater signature of the ship platform and other less well-known detection methods such as magnetic signature, bioluminescence, and wake and so on. It must be stressed from the outset that there has been a significant paradigm shift in warship design in the past two decades, which has been rather to move away from the view that it is simply nice to incorporate stealth into warship design as something of an affordable extra if possible. Instead stealth is now seen to be the critical component around which the warship is designed, and is certainly the case for the DD(X) Zumwalt-class surface combatant. However, it is the very cost of stealth that has made the Zumwalt a victim of its own stealth success, and mitigated against the future of the programme, in favour of a more traditionally tried and tested warships. The shift in emphasis towards stealth in current platforms is evidenced through the radical transformation of platform design between the RN Type 23 frigate and the latest stealth Type 45 Destroyer HMS Daring as well as the La Fayette-class frigate and Swedish Visby stealth class corvette built

by Kockums.

An able reader or student should be able to describe, discuss and analyse the ways in which modern and often highly complex sensors and communications systems can

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xii • Introduction have their performance degraded by hostile activities. We will consider the various design techniques which might be incorporated to negate the effects of these activities and to reduce likewise the overall probability of a ship’s detection.

Clearly stealth is only a part of the story, as a stealth warship cannot provide the same sense of intimidating power projection off the coast of a potential enemy if they do not know that you are there, and neither can stealth ensure platform safety and integrity once the first salvo is fired. Obviously there is still a significant role to be maintained in terms of self-protection of a platform, and the increased cost that stealth brings to the value of the ship asset is only likely to increase the required investment in ship’s defences, be they long- and short-range missile defence systems, a close-in weapon system (CIWS) or gun as well as various soft-kill methods at the ship’s disposal. Stealth can actually provide a range advantage over a variety of sensor systems, and the reduced signature provides a sufficiently ‘fuzzy picture’ that an enemy may at best detect you but will be quite unable to classify the threat correctly.

According to Merriam-Webster’s Online Dictionary, ‘stealth’ (pronounced: stelth) is derived from the thirteenth-century ‘Middle English stelthe; akin to Old English stelan to steal’, with several related meanings.

1 a archaic: theft b obsolete: something stolen 2 the act or action of proceeding furtively, secretly, or imperceptibly ‘the state moves by stealth to gather information – Nat Hentoff ’ 3 the state of being furtive or unobtrusive [and in the context we will be considering] 4 an aircraft-design characteristic consisting of oblique angular construction and avoidance of vertical surfaces that is intended to produce a very weak radar return Stealth technology is also known as low observable technology (LOT) and is a subdiscipline of ECM, which covers a range of techniques used not just with aircraft, but includes ships and missiles, in order to make them less visible (ideally invisible) to radar, infra-red and other detection methods.

There are also issues presented by the class of threat that the stealth warship has been constructed to deal with, as the most likely asymmetric threats that will present themselves to warships in the near future are the small (and ironically stealthy) fast boats manned by pirates, insurgents or terrorists, like those who caused damage to the USS Cole, an Arleigh Burke-class destroyer. The USS Cole was the target of a terrorist

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Introduction • xiii

▲ Figure I1 The USS Cole (DDG 67) is towed away from the port city of Aden, Yemen, into open sea by the Military Sealift Command ocean-going tug USNS Catawba (T-ATF 168) on 29 October 2000

attack in the port of Aden in October 2000, during a scheduled re-fuelling. The attack killed 17 crew members and injured 39 others, demonstrating that even a heavily armed high-tech platform is still vulnerable to relatively simple threats (Figure I1).

As the ancient Chinese general Sun Tzu wrote in his The Art of War, dating back to 450 BC and the world’s oldest treatise on military strategy, ‘All warfare is based on deception’, and certainly warships stealth and signature reduction techniques play an increasing component in that deception today. Stealth can generally be regarded as any technique used to reduce reflected sources of radiation, mostly with passive measures, whilst signature reduction involves methods designed specifically to reduce a ship’s own emissions – methods which are largely active. In reality, though, the terms ‘stealth’ and ‘signature reduction’ are used fairly interchangeably. The oldest and most successful recorded reference to deception before the modern era is that illustrated in the book of Judges (6–7) concerning Gideon who with 300 men, trumpets, torches hidden in jars and precision timing at the change of the enemy guard routed a much larger force.

15

When Gideon heard the dream and its interpretation, he worshiped God. He returned to the camp of Israel and called out, ‘Get up! The LORD has given the Midianite camp into your hands.’ 16Dividing the 300 men into 3 companies,

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xiv • Introduction he placed trumpets and empty jars in the hands of all of them, with torches inside … 19Gideon and the 100 men with him reached the edge of the camp at the beginning of the middle watch, just after they had changed the guard.

They blew their trumpets and broke the jars that were in their hands. 20The 3 companies blew the trumpets and smashed the jars. Grasping the torches in their left hands and holding in their right hands the trumpets they were to blow, they shouted, ‘A sword for the LORD and for Gideon!’ 21While each man held his position around the camp, all the Midianites ran, crying out as they fled.

You could even regard this as the first example of coordinated, network-centric warfare! Certainly the desire for ‘invisibility’ until the final moment of attack has been a key influence in how warfare has been conducted since ancient times. The military quest for invisibility appears in Greek mythology: Perseus’ helmet and Gyge’s ring both rendered their wearers invisible, useful when fighting monsters, and also formed the basis for the ‘One Ring’ in Tolkien’s famous trilogy The Lord of the Rings. However, such abilities no longer belong entirely in the realm of fantasy or science fiction such as Star Trek, as these days the world’s armed forces can draw on sophisticated stealth techniques to hide themselves from their enemies. Stealth technology seeks to render military ships, vehicles, men and aircraft ‘invisible’ to modern detection systems, such as radar and magnetic sensors, by reducing the levels of reflected radiation whilst at the same time lowering the craft’s own emissions (Figure I2). I will examine the various applied techniques that have been, and are likely to be, employed to make a platform less prone to detection. Certainly if these techniques are applied successfully, effective targeting, although perhaps not impossible, will be highly unlikely, whilst at the same time countermeasure systems will attempt to deny the enemy the tactical use of the electromagnetic spectrum (and acoustic spectrum) whilst retaining one’s own use of military spectral capabilities.

When it comes to an aircraft carrier or large battleship, this is no mean feat. Stealth works hand in hand with precision, and it is no accident that stealth aircraft today use precision-guided munitions to great effect. Stealth also works in partnership with modern decoy systems, as the harder it is to ‘see’ the real target, the more likely that a decoy system will be selected as the chosen target because of the larger more attractive signal it may provide. We will start our discussion of stealth with radar, a sensor many readers will be familiar with, followed by the visible spectrum, infrared spectrum, various other spectra and finally an examination of modern stealth ships themselves.

For me, the real issues of stealth are not driven by academic interest alone but in terms of considering the safety provided to a vulnerable crew at sea and the preservation and

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Introduction • xv

▲ Figure I2 Various signatures and cross sections © CR Lavers

security of our personal and national freedoms won at great corporate and individual cost. If I may paraphrase Sir Winston Churchill, I anticipate that for the crews of these ships in future conflicts, with the vast amount of dedicated research that has gone into UK stealth warship design, never before will so much be owed by so few to so many for their survival and perhaps the continued security of our nation and its traditions as well.

It is as true today as in yesteryear that ‘[i]t is on the Navy under the good providence of God that our health, prosperity and peace depend’ (Britannia Royal Naval College motto, above the main college doors).

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1

RADAR [A]head towards London I saw a small, tight formation of bombers completely encircled by a ring of Messerschmitts. They were still heading north. As I raced forward, three flights of Spitfires came zooming up from beneath them in a sort of Prince-of-Wales’s-feathers manoeuvre. They burst through upward and outward, their guns going all the time. They must have each got one, for an instant later I saw the most extraordinary sight of eight German bombers and fighters diving earthward together in flames.

John Beard, ‘Battle of Britain, 1940’ [1]

The story of modern radar and with it the radar technology to counter its effectiveness, ‘stealth’, is where we will begin, arising as it did out of the rearmament of Nazi Germany in the 1930s and the significant expansion of the German Luftwaffe. The British government was alarmed at the rapidity of these developments and soon realised that an aircraft warning system had to be developed and quickly deployed in the likelihood of imminent war. In January 1935, Sir Robert Watson-Watt was asked whether radio waves might be used to detect aircraft approaching the shores of England. Sir WatsonWatt wrote a brief memorandum to the Air Defence Subcommittee of the Committee of Imperial Defence to promote developments of radio direction finding (DF). Based on this letter and the supportive efforts of Sir Henry Tizard, a concentrated radar development programme began in England. In 1937, a prototype radio DF station (later called the Chain Home (CH) system; Figure 1.1) was built at Bawdsey Research Station for Royal Air Force (RAF) use. The CH station operated at a relatively low frequency of 22 MHz, and was able to detect propeller-driven aircraft at a modest 3,000 m elevation and under good atmospheric conditions as far away as 150 km in fine weather but, due to absorption of radar energy by weather fronts and rain, substantially less in

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2 • Stealth Warship

▲ Figure 1.1 Chain Home command

poor weather. Nonetheless, due to radar’s dramatic ability to increase detection range beyond the visible horizon and to provide a degree of positional information,

by September 1939, at the outbreak of war some 20 CH command stations were fully operational. The radar equipment used in the Battle of Britain was developed by a group of dedicated scientists initially based at the National Physical Laboratory in Teddington (still providing measurement standards to this day). Under the guidance of Sir Robert Watson-Watt (Figure 1.2), they were not only able to detect reflected radio waves from moving bomber aircraft but were also most importantly able to develop a system of practical operational procedures for using it.

This approach was vital and probably first realised by Sir Henry Tizard, who had been chairman of the committee on the scientific study of the defence of Britain that was responsible for launching Watson-Watt on the radar path. To tackle the problem, Tizard obtained use of the RAF’s No. 32 Squadron stationed at Biggin Hill in Kent. They carried out a series of trials using the first CH radar system, developing the control procedures to intercept unsuspecting targets such as civilian Dutch KLM airliners, but kept the radar emissions directed well away from Lufthansa flights to avoid alerting the Germans! The

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Radar • 3

▲ Figure 1.2 Sir Robert Watson-Watt

▲ Figure 1.3 German Heinkel He 111s which went into service in 1937

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4 • Stealth Warship procedures developed during this experiment were those later used by British aircraft controllers during the strategically important Battle of Britain fought fiercely from the summer of 1940 well into the autumn (10 July–31 October 1940) (Figure 1.3).

This was indisputably the first modern example of a network-centric warfare, where the assets of a significantly depleted RAF were able to be accurately vectored to intercept German bomber aircraft. This uncanny ability of the British RAF to intercept German Luftwaffe sorties led the German’s high command to gain the false impression that Britain had a much larger air force and was partly responsible for the abandonment of the planned Nazi invasion of Britain (Operation Sea Lion). It was this combination of the hardware and operational ‘software’ in use that made radar so vital and successful to the British. The German failure to achieve its objective of the complete annihilation of Britain’s air defences, or indeed an outright surrender, is rightly considered a critical turning point in the Second World War and stiffened British determination and defiance.

The basic principle of radar, or more strictly echo location, is quite simple. Visible light, of which we are all familiar, is but part of a wider family of waves which form the electromagnetic spectrum (Figure 1.4), covering waves such as X-rays, gamma rays and ultraviolet radiation which all have more energy than visible light and also waves of longer wavelength, such as infra-red (heat), radar and very low-frequency (VLF) waves used to communicate with submerged submarines.

If these electromagnetic waves are sent in the form of short pulses which strike an object with a flat surface, some of the wave energy transmitted from the radar will be reflected back to the radar receiver, similar to the optical dazzle observed from solar ‘glint’ off a sunlit window on a sunny day (Figure 1.5).

If the elapsed time t, from the transmission of a short radar pulse to the time the echo is received, is measured, the wave speed allows the contact range to be calculated accurately. As electromagnetic waves all travel at the same speed of light in vacuum, and only a little less in our planet’s dilute atmosphere (c = 3 × 108 m s−1), the distance they travel may be given as follows: distance = ct. Hence contact range R, which is half ct the total distance, is given as follows: R = __ .

2 For example, if the elapsed recorded electronic time from pulse transmission to reception is one thousandth of a second (or 1 ms), the radar range from the transmitter to the reflecting target will be as follows: (3 × 108 × 1 × 10−3) _________________ 2 m or 150 km distance

This relationship is used frequently in pulse radars to measure contact range, and the method is often referred to as ‘pulse delay ranging’. Other important radar parameters include the transmitted radar frequency (denoting the energy of the wave), the pulse repetition frequency or PRF (the number of pulses transmitted per second) and the pulse duration.

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Radar • 5 Frequency (Hz) 1019

Wavelength

Gamma-rays

0.1 Å 1Å 0.1 nm

1018 X-rays

1 nm

17

10

400 nm

10 nm 1016

Ultraviolet

500 nm 100 nm

1015 Visible

1000 nm 1 µm

Near IR 14

10

600 nm

10 µm

Infra-red 1013 Thermal IR

100 µm

700 nm

12

10

1000 µm 1 mm

Far IR 1000 MHz

1011 UHF

Microwaves 1010

500 MHz

1 cm

Radar 10 cm

109 VHF 7-13 100 MHz

Radio, TV

FM VHF 2-6

50 MHz

1m 108

10 m 107 100 m 106

AM 1000 m Long-waves

▲ Figure 1.4 Electromagnetic spectrum

Transmitted pulse

Reflected echo

▲ Figure 1.5 Pulse delay ranging © CR Lavers

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6 • Stealth Warship

Early Radar Stealth Modern warship radar stealth materials have much to thank concepts developed for earlier stealth aircraft. In Nazi Germany during the 1930s–1940s, two visionary aircraft designer brothers Walter and Reimar Horten developed a large number of aircraft, including aheadof-its-time proposals for a strategic bomber, envisaged as carrying a German-developed atomic bomb into the very heartland of America. The Horten H. IX designated the Horten 229 (Figure 1.6), fortunately developed very late towards the end of the Second World War, was built by Gothaer Waggonfabrik and structured around the use of radar absorbent glues and very low radar reflecting materials. It incorporated an extremely unusual low cross section flying wing concept, making this the first ‘flying wing’ powered by a jet engine.

The ‘flat’ profile of the aircraft made it more difficult to see against a cloud-filled sky than a conventional aircraft, and the more streamlined approach reduces aerodynamic drag to some extent, improving endurance or the range of the aircraft. The Horton project was given the personal approval of German Luftwaffe Reich Marshal Hermann Göring, with the intended performance requirements to carry 1,000 kg of bombs a distance of 1,000 km with a speed of 1,000 km hr−1, exhibiting the typical high-performance standards expected from German engineering of its time. The aviation ceiling was intended to be 15,000 m (49,213 ft). Ironically the flying wing concept, the actual aircraft and some of the engineers fell as the spoils of war to the victorious allies and was subsequently developed by Northrop in the United States of America on its YB-49 after the Second World War and the low observable ‘flying wing’ was born.

The idea of radar stealth was not alien to the British scientific establishment, who at the same time had also begun to experiment with early forms of radar absorbent material or RAM on its warships and also on the Canberra PR3 photographic reconnaissance aircraft of the early 1950s. The Canberra was developed from the B(2) light bomber as a replacement for the Mosquito PR34 reconnaissance aircraft, which had been used extensively during the Second World War. The RAM-coated Canberra aircraft were a much needed post-war response to the U-boat radar absorbing snorkel tubes developed by the German Navy. The next significant step forward in developing radar stealth technology is generally accepted to have taken place in 1954 when Kelly Martin at Lockheed was tasked by the US Central Intelligence Agency (CIA) to develop a covert spy plane (the genesis of the real ‘Project Rainbow’ which I will mention later), leading to the first U2 Soviet overflight in 1956.

The U2 had a network of thin wires with spaced ferrite beads (somewhat akin to an abacus) which absorbed energy and included specially fabricated ceramic

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Radar • 7

▲ Figure 1.6 Horten H. IX designs

▲ Figure 1.7 Shuttle heat tiles © CR Lavers

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8 • Stealth Warship wing leading edges, made of fibreglass and honeycomb plastic, skimmed or finished with heat-resistant fibreglass. Such developments in ceramic heat-resistant tiles have continued over the decades and led eventually to the technology being deployed on the series of US space shuttles (Figure 1.7), and which when damaged led to the devastation observed on the shuttle Columbia (1st February 2003). The U2 aircraft was a first step along the path of focused stealth aviation.

SR-71 The next step was the United States Air Force (USAF) order for a reconnaissance version of the A-12 Oxcart, originally designed for the CIA by Clarence Johnson at the Lockheed Skunk Works in December 1962, in the wake of a U2 lost over Russia and the infamous show trial of Gary Powers in Moscow. Originally named R-12, it was later renamed SR-71 (Figure 1.8). The US Defense Advanced Research Projects Agency (DARPA) was rightly concerned by the advances in Soviet-made surface-to-air missiles (SAMs). Certainly by the early to mid-1970s the Cold War was in real danger of going hot, with Soviet

▲ Figure 1.8 SR-71

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Radar • 9 nuclear testing and arms proliferation apace. There was a genuine climate of fear of the perceived Soviet missile build-up. The SR-71 was longer and heavier than the A-12.

Its fuselage was lengthened for additional fuel capacity and for increased range. A second seat was added to the cockpit and further reconnaissance equipment included intelligence sensors, a side-looking radar and a photo camera. The SR-71 ‘Blackbird’ first flew on 22nd December 1984 and was finally ‘retired’ from USAF service in 1998. The mission intent of the SR-71 was to provide the same sort of reconnaissance capability provided by the U2 programme, but it had the unique advantage with its Mach 3+ speed that if an enemy surface-to-air missile was launched and subsequently detected the aircraft could simply accelerate to outrun the missile! Thirty-two SR-71s were built, with none of them lost to enemy action, although 12 aircraft (a rather high number) were destroyed in a variety of accidents. Since 1976, the SR-71 has maintained its official record as the fastest air-breathing manned aircraft in the world.

Lockheed’s F-117A ‘Nighthawk’ (Figure 1.9) was the first operational aircraft to fully exploit stealth and was intended primarily to penetrate heavily protected environments at night with precision and accuracy. Named after the Nighthawk, a nocturnal bird, the likely time for deployment is intimated from the start. Competition for this first fully stealthy defence contract was extremely fierce, with bids submitted from both Lockheed and Northrop. Lockheed’s winning ‘Have Blue’ design was based on several sophisticated models of rotating plates in two dimensions. In 1975, Kelly retired and

▲ Figure 1.9 F-117A

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10 • Stealth Warship Ben Rich succeeded him to lead the think tank of brilliant aeronautical engineers designing the undesignable. Rich lobbied to get Lockheed into contention for the stealth design, having been surprisingly overlooked in spite of their successes with the U2 and SR-71. In 1975, Lockheed’s Advanced Design and Skunk Works prepared a proposal for the Experimental Survivable Testbed (XST) programme. This Lockheed XST programme was named ‘Project Harvey’ after the 1950 movie Harvey, staring James Stewart, about an invisible 6 ft rabbit that could only be seen by Stewart. Dick Scherrer was the Project Harvey programme manager and Leo Celniker the manager for the XST proposal, which led to the ‘Hopeless Diamond’ model.

Skunk Works engineers began working on an aircraft which would have a vastly reduced radar cross section (RCS) compared with existing jet engine aircraft that would make it all but invisible to enemy search radars but would still be able to fly and carry out combat missions in various Cold War, long-range strategic nuclear scenarios.

It had generally been accepted since the inception of the jet engine, with its metal intakes and metal supporting frame, that aircraft would always be easy to detect with radar because of strong reflections from flat metal surfaces. The objective of the Skunk Works team was to take this rule and to turn it on its head. Alan Brown, a brilliant English engineer, was given the task to lead the group trying to reduce the RCS created from the

▲ Figure 1.10 Comparison of the two best known stealth platforms, the B2 and the F-117A, can be very illuminating

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Radar • 11 intakes. He found that a fibreglass grid absorber reduced the RCS significantly. He named this grid, tongue-in-cheek, the ‘Roach Motel’, after a US-bug-killing advert of the period with the classic line ‘The Roach motel – roaches check in but they don’t check out!’.

The key technique the Skunk Works team developed to counter this ‘immutable fact’ became known as ‘faceting’, in which ordinary airframe smooth surfaces were broken up into multiple triangular flat surfaces. These many surfaces were then arranged so that the majority of the radar energy incident on the aircraft would be scattered away from the aircraft at unexpected angles, leaving little energy, if any, to be reflected directly back into the enemy radar receiver. All lines and surfaces were designed with shallow inclination to the radar using huge mainframe computers with a memory found in most hand-held calculators today. There were so many surfaces that it took months to model the flat diamond shape which had no aerodynamics. The challenge was to cut bits out from the flat diamond to create a delta wing aircraft, which provides the United States with a global outreach and a lead in technology over the Soviet. At this time, the majority of radar systems developed relied on a radar whose antennae would not only transmit the outgoing pulse but would also be responsible for gathering the weakened reflected wave. Subsequent development of bistatic radar (where a radar transmitter and radar receiver are in two separate locations) and multistatic radar (where there are multiple separately located radar receivers) have provided further refinements of these earlier solutions.

An additional reduction in stealth fighter RCS (Figure 1.10) was obtained by covering the whole aircraft surface with RAM. However, the downside of faceting on aerodynamic surfaces was that it tended to produce an aircraft which was inherently unstable about all three of its major axes – roll, pitch and yaw!

The programme had the highest level of security; even the buildings where the research team worked had no windows, and only a minimum number of government people knew of the programme. Only a few of the Lockheed staff even knew the programme existed. The intent was to build two aircraft, one to test its flying qualities (which appeared for some to be very questionable) and another to test its stealth attributes.

Measuring Stealth James Clerk Maxwell (1831–1879), a Scottish physicist who conducted revolutionary work on electricity and magnetism, had in the previous century derived various equations that predicted in a clear way how a regular body of a given shape would

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12 • Stealth Warship reflect or scatter electromagnetic waves. With the help of a 1966 paper Method of Edge Waves in the Physical Theory of Diffraction published by a Russian physicist Pyotr Ufimtsev at the Moscow Institute of Theoretical Physics (and now at the time of writing, running a small one-man company Electromagnetics Research in Los Angeles), a paper which was largely ignored in the then Soviet Union, two Skunk Works engineers Bill Schroeder and Denys Overholser figured out the key maths behind stealth control surface design. Schroeder sketched an aircraft with no curved surfaces at all, except those of relatively small radius, with straight edges to its wings and tail surfaces. It was as if a diamond had been cut into the crude outline shape of an aircraft, albeit a fairly unaerodynamic looking one. Schroeder took the problem to Denys Overholser, an able software engineer who could think outside of the frame of what already existed. Using the number-crunching capability of an at that time state-of-the-art Cray computer, Overholser developed a computer program that modelled scattering from Schroeder’s new and peculiar faceted shapes, and predicted their theoretical RCS. However, it would not be satisfactory to stop with just the output of unvalidated computer models, but in true engineering fashion it required testing to prove the validity of these models. From the computer program, engineers created a 10 ft wooden model dubbed the ‘Hopeless Diamond’, which was taken to a secret outdoor radar test range in the Mojave Desert near Palmdale. The model was mounted on a 12 ft pole, and the radar dish placed 1,500 ft away. Apparently, if the anecdotal test reports are to be believed, the site radar operator could not see the model on the radar until a black bird landed right on top of the model. The radar detected the bird but not the aircraft scale model!

Some introduction needs to be made to the often quoted size of a target on a radar system. Unlike the familiar size of an object that we can see in the visible part of the electromagnetic spectrum and physically measure with a metre ruler, things are not quite so obvious in other parts of the electromagnetic spectrum. The size of a target’s image on radar is measured by its RCS, often represented by the symbol σ and is expressed in square metres. However, this ‘area’ does not equal its geometric area. A perfectly conducting sphere of projected cross-sectional area 1 m2, that is, diameter of 1.13 m, when measured on a test rig will be found to have an RCS of 1 m2 (or as close as likely to occur within experimental error!). A test aircraft returning twice as much energy as the test sphere would be said to have an RCS of 2 m2. Similarly a square flat plate of area 1 m2 will have an RCS of σ = 4πA2/λ2 = 13,982 m2, where A is area and λ is the wavelength at 10 GHz if the radar is set to transmit pulses perpendicular to the flat face [2]. At offnormal incident angles, energy is reflected away from the receiver, thereby reducing the RCS. So a small plate can generate a massive echo signal or RCS on the ‘enemy’ radar display.

Consequently, by appropriate choices of material, shape and size, a typical fighter aircraft having an actual area of 10 m2 when directly facing the radar system could

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Radar • 13 return much less energy than the echo energy returned by a test sphere returning an RCS of even a few square centimetres, thus bearing no relationship to the actual area of the plane in real life. The inherently unaerodynamic ‘brick’ shape of the Hopeless Diamond was superseded by the ‘continuous curvature’ approach of the B2, a larger aircraft yet with a smaller cross section and with a shape lending itself to a more aerodynamic platform.

Maximum Detection Range (MDR) and Radar Cross Section An individual search radar set’s MDR depends upon several factors such as transmitted power, the target’s reflecting properties, the antenna or aerial size and the receiver’s sensitivity. The MDR is given by simplifying the standard radar range equation, to find the maximum range a radar will detect a chosen target of a given size [3]. _______

PGσtotAeff MDR = _______ (4σ)2S

√

4

min

Here, P is the average transmitted power, G is the antenna gain, σ is the RCS of the chosen target (a measure of the contact size seen by the radar beam), tot is the time the contact is illuminated by the radar beam, Aeff is the effective size of the receive antenna and Smin is the minimum signal energy required for detection by the receiver.

Any change in these parameters will change the MDR. Generally speaking, wave loss increases with increasing frequency and so MDR will fall. Clearly, the ship’s search radar has control of all but the elusive RCS of the chosen target. However, from the radar operator’s perspective trying to counter stealth, a suitable combination of these five factors can counterbalance a moderate reduction in the airplane’s overall RCS. It is quite possible for a fire-control radar, with a highly directional beam (or high gain antenna) and a moderately high power level to track stealth aircraft and even potentially engage them successfully as evidenced by the F-117A taken down over Bosnia (believed to be due to a modified surface-to-air battery SA3 or SA6 and initial intelligence of the planned flight path, which was thought to be similar to a previous flight). It was also believed subsequently that with the Soviet help and clever algorithms the Serbs had used the radar to detect the ‘lack of aircraft reflectivity’ against its background. The aircraft was destroyed on 27 March 1999 during the NATO bombing of Serbia after the aircraft was shot down in combat 25 miles west of Belgrade, with pieces shown on Serbian TV. There have been at least six notable incidents of stealth aircraft losses, including a very public black jet loss at the Baltimore air show in September 1997 with

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14 • Stealth Warship an aircraft disintegrating in mid-air and crashing to earth in an urban area. Miraculously no one was killed. However, the most potent threat since the Vietnam War to any aircraft lies in the realm of infra-red heat-seeking systems which we will briefly consider later.

Interestingly, it was believed that Serbian forces had received considerable help from Russian intelligence officers regarding the downing of the F-117A and were quick to swarm over the remains of the aircraft looking for surviving salvageable parts, including bits of first-generation US stealth materials. Russian interest lay in the subsequent analysis of the frequency-dependent response of such stealth materials in order to find frequencies or, one might say, weaknesses, in response for which the F-117A would be more vulnerable to detection.

In addition, the radar range equation shows that __

MDR √ σ 4

So a 16-fold reduction in RCS will only result in a meagre halving of the platform’s overall MDR. It is thus obvious why there is so much emphasis to significantly reduce the RCS (to produce even a moderate reduction in MDR), and the RCS of a modern stealth fighter (or bomber) really needs to be equivalent to a very small bird for it to operate in the way that it does currently. The relationship between MDR and RCS can also be exploited to help make decoys operate more effectively. The concept of a decoy here is the same as that for luring or enticing a person or animal away from an intended course, typically into a trap. The decoy is designed to provide a more attractive target to the targeting enemy missile. In the case of radar, several passive radar decoys exist on common naval warfare usage, some even having the ability to ‘break the lock’ of an already successfully locked on radar-guided missile.

One such radar decoy, chaff or Window, was originally developed by the British during the Second World War and is a radar countermeasure which when launched from a small rocket will spread a cloud of small, thin pieces of aluminised nylon or metallised glass fibre which will appear as distracting or confusing alternative targets on the radar operator’s display screen. The use of Window proved extremely important during the Normandy D-Day landings where chaff was used to confuse the defending Germans of the intent of the embarked maritime allied forces. An alternative radar decoy involves the use of permanently floating deployed ‘corner reflectors’, just larger versions of those used by merchant shipping and private yachts to show up better on radar due to their strong direct reflected signal; however, a permanent fixture that reflects well, even if it is towed along behind a ship, is not necessarily a particularly good idea as it will give the ‘enemy’ an approximate location of a possible target which it might otherwise not have. A more practical arrangement involves the timely launch and deployment of an inflatable corner reflector, which will provide a large alternative RCS only as and when

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Radar • 15 required in the close vicinity of the ship. Many navies of the world now possess the ability to launch chaff rounds routinely.

In any case, the ship would be well advised to turn to face a threat rather than sitting ‘broadside’ as this will enable the ship to not only be in a better place to ready its own weapons and layered defence but will also be operationally reducing its RCS at the same time. For example, a stealth frigate with a cross section of perhaps 2,500 m2 broadside on could have a bows cross section when facing the threat of as little as 400 m2. Such a manoeuvre will aid the effectiveness of any deployed chaff as this is then hopefully the source of the largest reflected radar signal. These sort of changes in cross section are often best expressed in engineering notation in terms of decibels: S

2 dB = 10 log__ S 1

where S2 is the final or second signal level and S1 the original signal level we are comparing it with. In this case, dB = 10 × log(400/2,500) = –7.96. The minus sign in –7.96 dB shows there has been an overall signal loss or negative gain. The received radar echo power is nearly 8 dB down compared to the broadside return. This is expected as only a small fraction of the transmitted electromagnetic energy will be reflected back from the smaller tilted bows of a ship and its forward-facing superstructure rather than the large flat sides of the ship.

In 1977, Lockheed received a contract from the Defence Advanced Research Projects Agency (DARPA) for the construction of two 60% scale test aircraft under the project title ‘Have Blue’. Shortly after, the Have Blue contract was transferred over to US Air Force System Command control and became ‘black’, with all information about it being highly classified and restricted to those only with a legitimate need to know. Outside of a few people at Lockheed and the Defense Department, no one in fact knew that Have Blue even existed!

The two Have Blue aircraft were built at Lockheed in a few months. With so much hinging upon the development of new and as yet unproven stealth technologies, the intention was to design the rest of airframe as conservatively as possible, which also helped to reduce the development time and avoid unnecessary suspicions of what was really going on. The first was intended to evaluate its flying characteristics, whereas the second was to evaluate the platform’s all critical radar signature. Existing off-theshelf components were used where feasible. The engines used were a pair of standard General Electric J85s, mounted in the enclosures above the wings. The main landing gear was also taken from a Fairchild Republic A-10, and various fly-by-wire (FBW) components were ‘borrowed’ from an F-16 whilst the instrumentation and ejection seat were taken from a Northrop F-5. Have Blue aircraft had the same general shape

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16 • Stealth Warship as that which would later become familiar with the F-117A, except that the rudders were located forward of the exhaust ejectors and angled in rather than out. The leading edge of the semi-delta wing was swept back at a daring 72.5°. The wing featured two inboard trailing edge elevons for both pitch and roll control. There were no flaps or speed brakes but fortuitously an ejection seat was provided!

The Have Blue aircraft were equipped with the latest FBW flight controls that had been adapted from the existing F-16 system airframe. However, the system did have to be modified to handle an aircraft that was unstable about all its three axes (the F-16 is unstable only about the pitch axis). The problem of designing a stealthy system for airspeed measurement had yet to be solved, but an inertial navigation system provided enough speed data for test purposes when aircraft probes were retracted. The flight attributes of the plane were heavily controlled by advanced computer software such that the plane can be thought of as almost flying by itself, with the pilot largely managing the systems and checking critical factors such as fuel, time, speed and so on. Once committed to its initial attack axis, the plane was locked in to complete its bombing run.

Two prototypes were built at a modest cost of US$37 million. Lockheed workers assembled the Have Blue aircraft in a cordoned-off area in Burbank, California, beyond the prying eyes of the general public and indeed most Federal employees. Neither aircraft received an official Department of Defence (DoD) designation, nor did they get a USAF serial number. However, Lockheed gave each aircraft its own serial numbers, 1001 and 1002. The first example (1001) was finished in November of 1977. In order to keep the project away from spying eyes, the Have Blue prototype was then shipped out to the Groom Lake Test Facility in Nevada (so-called Area 51) in high secrecy for test flights in a remote area of the Nellis test range complex, a good location for testing secret aircraft. A camouflage paint scheme was applied to make it hard for unwanted observers at Groom Lake to determine the aircraft’s shape. The first flight of the Have Blue took place in January or February of 1978 (the exact date is still classified), with Lockheed test pilot William M. ‘Bill’ Park sitting at the controls. Flight test of the Have Blue initially went smoothly, and the FBW system functioned well. Landing speed was relatively high (160 knots) and as expected because of the lack of flaps or brakes in the platform’s construction. However, on 4 May 1978, Have Blue prototype number 1001 was landing after a routine test flight when it hit the ground a little too hard, jamming the right main landing gear in a semi-retracted position. Pilot Bill Park pulled the aircraft back into the air and tried to shake the gear back down. However, after his third attempt failed, he was ordered to take the aircraft up to 10,000 ft and eject. Park ejected successfully, but in the process he is reported to have hit his head and was knocked unconscious. Since he was then unable to control his parachute during descent, his

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Radar • 17 back was severely injured on impact, but he did survive. However, his injuries prevented him from continuing his test pilot career, and he was unfortunately forced to retire from flying. The Have Blue aircraft, incidentally, was destroyed in the crash.

Have Blue 1002 arrived at Groom Lake shortly after the loss of 1001. It took to the air for the first time in June 1978, with Lt Col. Ken Dyson at the controls. From the mid-1978 to early 1980, Lt Col. Dyson flew more than 65 different test sorties, testing the response of the aircraft to various radar threats. The Have Blue prototype 1002 proved to be undetectable by all airborne radars except the Boeing E-3 AWACS, which could acquire the aircraft at only short range. Most ground-based missile tracking radars could detect the Have Blue only after it was well inside the minimum range for the surface-to-air missiles with which they were associated could engage. Neither ground-based radars nor air-to-air missile guidance radars could lock onto the aircraft, and it was found through experience that the best tactic to avoid radar detection was to approach the ground radar threat head on, presenting the Have Blue’s small nose-on signature.

Application of RAM to the airframe proved to be rather difficult, and ground crews had to seal all the aircraft’s joints thoroughly before each and every flight. Early F-117A RAM came in linoleum-like sheets, cut to shape and bonded to the skin to cover large areas. Doors and access panels were carefully checked and adjusted for a tight fit between flights, and all gaps were filled in with conductive tape and covered with more RAM. Paint-type RAM was available, often called radar absorbent paint (RAP), but it had to be applied by hand. The paints used were and are generally toxic to human (and indeed animal species). Even the gaps around the aircraft canopy and the fuel-filler door were filled with RAM paint before each flight. Ground crews would check that all surface screws were sufficiently tightened, as even one loose screw in an access panel could potentially make the aircraft show up during radar signature tests. Consequently, meticulous attention to detail was the ‘signature’ of the aircraft’s success, from the honeycomb RAM on the wing edges, inlets, exhaust, nozzles, holes to door seals, which increased the demands on the supportive ground crew staff beyond that normally required for normal ‘non-stealthy’ military aircraft. The aircraft had six skin layers, absorbent adhesives, tapes and putty, and sub-elements of ferromagnetic coatings in a high dielectric plastic. Although this method is used in naval design, the B2 and the F-35 (Lightning) Joint Strike Fighter (JSF) use enhanced software prediction methods to create radically different aircraft shapes than the much earlier, and simpler by comparison, F-117A. Have Blue 1002 was finally lost in July 1979 during its 52nd flight with Lt Col. Dyson still at the controls when one of its J85 engines caught fire.

The fire became so intense that the hydraulic fluid lines burned through, and Lt Col. Dyson was also forced to eject, with the loss of the 1002 prototype as well. The result was that within 8 months both aircraft were gone! Nonetheless, the value of stealth had

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18 • Stealth Warship been proven. As a further note, it should not be a great surprise to the more thoughtful reader that the reporting of unidentified flying objects (UFOs) in this vicinity has been a common occurrence since this time of early stealth fighter testing. Fortunately for the Lockheed team they had already gathered about 90% of their evaluation data to ‘green light’ the project. The loss of aircraft at an early stage, with the civilian arm of Lockheed going through a lean period, would almost certainly have meant a deletion of the programme, and a loss of the world’s first true stealth fighter.

The Air Force awarded a contract to the Lockheed ‘Skunk’ Works to develop the ‘Senior Trend’ aircraft, with the secret top brass finding US$340 million of covert funds to allocate to it. Initial F-117s were delivered in June 1981, with only the facetted intersecting plates of its radar reducing airframe hinting to the informed observer at its potent stealth features. This project was shrouded in secrecy, probably rivalled only by that of the Manhattan Project team that developed the atomic bomb and led by Robert Oppenheimer. From 1982, the 4450th Tactical Group operated the F-117 from its Tonopah Test Range. This covert facility enabled the development and production of F-117 to continue far from watchful eyes. Under the cover of testing new weapon systems on attack planes, which were indeed flown up and back from Tonopah, the flight crews flew the aircraft under the cover of night, which during the daytime were kept hangered to avoid detection by satellite imagery and other advanced Soviet technologies. Even the hangers cost £200 million to ensure the highest level of security. In October 1989, the 4450th became the 37th Tactical Fighter Wing, which continued to operate F-117s through its first combats. In December 1989, two of the ‘black jets’ participated in ‘Operation Just Cause in Panama’. During this US invasion, Panamanian general Manuel Noriega was deposed, with Guillermo Endara sworn into office as president-elect. The aircrafts were originally meant to target barracks loyal to Noriega, but at the last minute the target was switched (fortunately for the Panamanian troops) to drop two 2,000 lb bombs on the fields next to the barracks to demonstrate United States’ air superiority. Due to the media portrayal of ‘dropping bombs on fields’ that followed, US Congress was initially critical of the cost involved: US$8 billion for 59 planes and spares.

Following the Desert Storm campaign – where the F-117A Night Hawk stealth fighters, just 2% of the attack force, dropped 40% of the bombs – F-117s were fully integrated into the Air Force arsenal. By mid-1992, the F-117 Wing transferred operations to Holloman Air Force Base in Alamogordo, New Mexico and re-designated the 49th Fighter Wing.

The F-117 Nighthawk’s first flight took place in 18 June 1981 and conducted USAF service from 15th October 1983 to its recent retirement in April 2008. Fifty-nine F-117A aircraft were built at a cost of US$111.2 million per aircraft! The USAF retired the F-117 primarily because of its introduction of the F-22 Raptor and also of the impending introduction

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Radar • 19 of the F-35 Lightning II, both aircraft offering increased capability and improvements in stealth technology. A final interesting story of the F-117A lies in the F designation itself.

Early on, after the F-16 cockpit had been chosen for the small stealth bomber, it was realised that no fighter pilot worth his salt would switch to a ‘B’ designation (bomber) from an ‘F’ designation (fighter). Hence the need to label the plane with an ‘F’ designation, although it has no ‘fighting ability’ or ‘defences’ of it own other than its stealth!

Stealth Approaches In simple form, radar stealth consists of three basic techniques that should be used to complement each other: 1. Materials should be incorporated into the ship’s superstructure and outside surfaces that have a very low radar reflection coefficient, such as plastics, carbon composites or glass-reinforced plastic (GRP). Surprisingly perhaps Nelson’s flagship HMS Victory, in spite of its extensive mast rigging (Figure 1.11), would have a relatively low RCS by modern ship standards!

2. RAMs – usually foams which can be overlaid with specialist paints – are also generally included where possible. Simple RAM cancels any threat or ‘enemy’ reflected waves destructively with the application of quarter wavelength coatings. Multiple RAM layers, a little like the structured layering seen within plywood, can also be applied to provide destructive cancellation across a broader range of wavelengths. Surface paint may also add carbonyl iron ferrite spheres so that incoming radar waves induce alternating magnetic fields in the surface paint, converting radar energy into heat. This type of paint is often referred to as ‘iron ball’ paint. Conductive transparent coatings also allow the designer to have the flexibility to introduce controlled shapes that can deflect radar waves so that they do not even enter a ship’s bridge windows and then reflect off in a different direction away from the roving eyes of the enemy radar. Gold and transparent indium tin oxide (ITO) are also frequently used.

RAM is usually composed of a combination of dielectric and ferromagnetic materials.

Dielectrics can be thought of as slowing waves down, whilst ferromagnetic materials will absorb them. A high-frequency, anti-reflection coating on a low-frequency, wideband structure will absorb most of the energy, analogous in some ways to a peacock’s feather where constructive interference coatings rest on a black broadband absorber giving the peacock its familiar appearance (Figure 1.12). However, whilst the

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An Essential Introduction to Stealth Technology

www.adlardcoles.com

Published by Adlard Coles Nautical an imprint of Bloomsbury Publishing Plc 50 Bedford Square, London WC1B 3DP www.adlardcoles.com Copyright © Christopher Lavers 2012 First published by Adlard Coles Nautical in 2012 ISBN 978-1-4081-7525-5 ePDF 978-1-4081-7553-8 ePub 978-1-4081-7552-1 All rights reserved. No part of this publication may be reproduced in any form or by any means – graphic, electronic or mechanical, including photocopying, recording, taping or information storage and retrieval systems – without the prior permission in writing of the publishers.

The right of the author to be identified as the author of this work has been asserted by her in accordance with the Copyright, Designs and Patents Act, 1988.

A CIP catalogue record for this book is available from the British Library.

This book is produced using paper that is made from wood grown in managed, sustainable forests.

It is natural, renewable and recyclable. The logging and manufacturing processes conform to the environmental regulations of the country of origin.

Typeset in 10.5 pt Baskerville by MPS Ltd Printed and bound in the UK by MPG Ltd Note: while all reasonable care has been taken in the publication of this book, the publisher takes no responsibility for the use of the methods or products described in the book.

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