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Electromagnetic Pulse-From Chaos To A Manageable Solution AUTHOR Major M. CaJohn, USMC CSC 1988 SUBJECT AREA C4 EXECUTIVE SUMMARY TITLE: ELECTROMAGNETIC PULSE-FROM CHAOS TO A MANAGEABLE SOLUTION I. Purpose: Alert our military and civilian personnel that elec- tromagnetic pulse (EMP) is an enemy to our survival, and investigate how we can defeat this foe with current equipment and technology. II. Problem: Although EMP has been known to exist for many years, its catastrophic impact on our strategic and tactical communications systems and weapons, as well as our civilian communications systems are not widely understood or accepted. Acceptance of this problem is being absorbed in the military establishment; however, the civ- ilian sector is slow to respond. III. Data: Escalation between the United States (US) and Russia reach an insolvable solution. Russia launches a nuclear missile attack; however, before the US can retaliate Russia explodes a high altitude nuclear weapon which renders the US's retaliatory capabil- ities useless. All aspects of EMP and the systems it attacks are described in detail. The effects of EMP are explored from the naivete of our scientists to the comparison of EMP to lightning. Interest grows within our country to defeat this enemy and the leading agency is the military. The military establishes testing facilities to learn about the effects of EMP. The results of these testing facilities are hardened programs for our strategic communications systems and weapons. The Army established a program that ensures all new equipment will be designed to be EMP hardened. The military has made significant strides in the strategic field and is attacking the problem in the tactical arena. However, the civilian community is lacking in a commitment to defeat EMP. Solutions to the problems of EMP are proposed using today's equipment and technology. IV. Conclusions: EMP can be defeated. The military has a sound and viable program in its strategic communications systems and weapons; however, the military must emphasize an EMP training and field expedient program in its tactical communications systems until EMP hardened equipment is procured. The civilian sector has no EMP program and must get one to ensure it can survive an EMP environment. V. Recommendations: Military leaders must stress and implement an EMP training and field expedient technique program. The military must continue to procure strategic and tactical equipment that is EMP hardened. Government agencies must encourage our civilian sector to build new communications systems that will withstand an EMP environment. ELECTROMAGNETIC PULSE-FROM CHAOS TO A MANAGEABLE SOLUTION OUTLINE Thesis Statement. Although electromagnetic pulse will disrupt or destroy essential communications systems, it is possible to establish a manageable and survivable communications system, which will ensure the United States can survive a nuclear attack. I. Nature of EMP A. What does a nuclear weapon produce 1. Surface burst (EMP) 2. High altitude EMP (HEMP) 3. Source region EMP (SREMP) 4. System generated (SGEMP) II. Effects of EMP A. Initially no scientist anticipated the serious effects of EMP B. Detonation of a nuclear device over Johnston Island produced disastrous effects in Hawaii C. Concerns of EMP on high tech communications D. Compare EMP with lightning III. Remedies for the effects of EMP A. The growth of interest in the U.S. B. U.S. builds test facilities to counter EMP C. Two ways to protect communications systems from EMP IV. Current EMP hardening programs A. The Army's program B. Strategic systems that are being EMP hardened 1. Communications systems 2. Aircraft 3. Weapons V. Problems remaining A. Civilian industry has no regard for EMP B. Military's lack of tactical communications systems that is EMP hardened VI. Proposed solutions A. FEMA conducts a study for the civilian sector 1. Must make recommendations 2. Must have a cost estimate B. Military must stress 1. Training 2. Practice field expedient measures VII. Summary A. EMP is a threat to unprotected communications systems B. Military must establish sound EMP management and main- tenance programs to neutralize the effects of EMP C. Problems can be conquered, but need more emphasis by our nation's leaders in the civilian and military communities ELECTROMAGNETIC PULSE - FROM CHAOS TO A MANAGEABLE SOLUTION Tension between the United States and the Soviet Union reaches new heights as both countries counter each others offensive moves. The Soviet Union initiates the first move when it masses thirty divisions along East Germany's western border during a time when there are no field exercises scheduled. The United States counters this move by placing the Fifth and Seventh Corps on alert and placing them in their forward defensive positions, and the United States begins the mechanism to mobilize its reserve. The Soviets counter this act by massing another twenty-five divisions along Yugoslavia's western border, which gives them the capability to strike quickly and deeply into Italy. The United States counters this by deploying the 82nd Airborne and the 101st Air Cavalry divisions to bolster the Italian defense. The United States puts its maritime strategy into action by deploying four aircraft carrier battle groups into the Norwegian Fjords. The Soviets counter this show of force by bringing all their nuclear attack submarines and missile launching submarines into their "homeland" protective waters. Each country's leaders use the "hot line" attempting to defuse this major crisis. The leaders of the super powers agree to launch a spy satellite to collect information and monitor each country's moves. In accordance with the space agreement the satellites are registered with the United States Space Command and both satellites are launched at the prescribed time. Three days later the tension between the two super powers ebbs. Then at 0500 Eastern Daylight Time the United States early warning satellites suddenly detect several Russian nuclear missile launchings from two Typhoon submarines (one on each coast). An alert is sent to the United States military commands around the world. The Ballistic Missile Early Warning System (BMEWS) now tracks the incoming missiles and predicts their impact points within the Con- tinental United States. The President of the United States is awakened and appraised of the situation. The president initiates a telephone conference call between the various unified and specified commands. Meanwhile, the Russian spy satellite, 500 kilometers over the central United States, explodes with a 400 kiloton force generating a high energy electromagnetic pulse covering the entire United States. The president orders a massive retaliation by the United States' triad forces, but nothing happens. The United States triad of Air Force bombers and missiles, and the Navy's Trident submarines stand by awaiting orders to launch; however, their communications systems are inoperative. Both military and civilian communications systems are crippled or de- stroyed by the electromagnetic pulse. Although electromagnetic pulse will disrupt and destroy essential communications systems; it is possible to establish a manageable and survivable communications system, which will allow the United States to survive a nuclear attack. The effects of electromagnetic pulse (EMP) warrant increased efforts to neutralize their potential to create chaos with communi- cations systems. EMP, is a killer of unprotected electrical and electronics equipment. Its effect of inducing extremely large and very rapid surges of voltage and current through electrical conducting materials offer unique leadership and engineering challenges to our country. With its current nuclear strategy of flexible response and controlled escalation, the United States places great reliance upon its command, control, and communications systems. However, the most vulnerable component of the United States is the same command, con- trol and communications systems that is so essential. This weakness in our command, control and communications systems is exactly what the Soviets will attack. Indications are that the Soviets will probably use a high-altitude nuclear burst to generate enough EMP to completely destroy or incapacitate the civil and military communications systems, missiles, aircraft control systems and radar systems(12:2-6-8). This analysis further indicates that EMP effects are integrated into Soviet strategic and tactical planning, especially at the outset of any nuclear exchange, as the Soviets always plan to use nuclear weapons at their choosing and not as a retaliatory response (13:2-4). The U.S. military was slow to realize the vulnerability of its command, control and communications systems. Nevertheless, improving this communications network is now the number one priority among all new strategic programs. In this paper, I will describe the nature of EMP, its effects and remedies for them. In addition, I will highlight two problem areas and pose solutions to them. The EMP threat is solvable, as there is enough scientific and engineering knowledge currently available to insure the survivability of communications systems from EMP effects. The detonation of a nuclear weapon produces several direct outputs in the form of neutrons, electrons, fission fragments, bomb debris, alpha particles, gamma photons and x-rays. In addition, the interaction of the gamma rays and x-rays with the atmosphere creates the indirect weapon effects of electromagnetic pulse (2:116-121). EMP is a pulse of electromagnetic energy of extremely short duration. Initially called radio flash, EMP is similar to the simultaneous transmission of a large number of radio waves varying from one KHz to 100 MHz and peak field amplitudes produced are very large on the order of 50 kilovolts (kv) per meter (4:72 and 9:1-20). The formation of EMP results from the collision of the gamma photons emitted from a nuclear detonation and interacts with atoms in the outer atmosphere. This results in the ejection of electrons and the creation of a strong ionized area referred to as the source field region. This complicated process occurs in a few billionth's of a second (nanoseconds) and last one millionth of a second (millisecond), which produces a strong electric field that radiates away from the source region (4:72-74). This radiated field is EMP. A number of parameters including the yield, its height-of-burst, asymmetries in the earth's atmosphere, and location of the burst relative to the earth's magnetic declination directly affects both the shape or coverage area and the strength of the EMP (9:1-1-2-11). Based on analysis of the various combinations of the preceding parameters there are four significant types of EMP. The first, surface burst electromagnetic pulse (EMP), occurs when the nuclear burst explodes on the earth's surface or up to two kilometers above the surface. The radiated wave is only propagated to a distance of ten to twenty kilometers from the burst point due to the higher density of the lower atmosphere. Although the area over which the low-altitude EMP produces a damaging effect is relatively small, it is significant on the tactical nuclear battlefield (9:1-10-1-11). The second type, high-altitude EMP (HEMP), is the most significant and, potentially, the most hazardous to our security. The explosion of a nuclear burst at an altitude greater than 30 to over 500 kilometers above the earth's surface will produce the above scenario. Due to the very thin to non existent atmosphere at these altitudes, the gammma rays emitted from the explosion will travel radically outward for long distances. Those gamma rays traveling toward the earth's atmosphere are stopped by collisions with atmospheric molecules at altitudes between 20 and 40 kilometers. These collisions generate Compton recoil electrons which interact with the earth's magnetic field to produce a downward traveling electromagnetic wave. This high altitude burst will not generate any other nuclear effect at the earth's surface (9:1-5). However, this type of nuclear explosion also produces a vast ground coverage. Significant HEMP levels occur at the earth's surface out to where the line of sight from the burst contacts the earth's surface. Consequently, a nuclear burst over the central part of the United States at an altitude of 500 kilometers would produce an EMP field that would incapacitate all communications systems in the continental United States (9:1-8). The third type of EMP is source region EMP (SREMP). This is produced by a nuclear burst within several hundred meters of the earth's surface (the fireball touches the ground). SREMP is localized three to five kilometers from the burst. The generation of EMP by a surface blast begins with the gamma rays traveling radically outward from the burst. This action causes the Compton electrons to move radically outward and leaves behind immobile positive ions. This produces an electric field and lasts two to three nano seconds. The final result is a tremendous surge on current in the air on any communications equipment and the SREMP renders the equipment useless (9:1-10-13). The last type of EMP is system generated EMP (SGEMP). SGEMP results from the interaction of x-rays or gamma rays striking an atom on a metal object. A nuclear blast in outer space sends gamma rays or x-rays out in all directions. If these rays were to strike an unprotected satellite or missile traveling above the atmosphere, these rays would knock out electrons from the atoms of the metal skin. This action would induce an EMP field that would make the satellite and the missiles useless (9:1-17-1-21 & 5:75-76). Although the EMP effect was known to exist during the detonationtion of conventional explosives prior to the first atomic explosion and was predicted in nuclear weapons' tests, the extent and potentially serious nature of EMP were not realized for several years. Several incidents related to the 1963 detonation of a 1.4 megaton nuclear device 250 miles above Johnston Island highlighted the potential effects of EMP. Immediately following the detonation, the island of Oahu, Hawaii, which was located 800 miles from ground zero, experienced several power outages, the activation of hundreds of burglar alarms and the short-circuiting of thirty strings of streetlights (1). EMP is of great concern today. As the field of electronics has evolved from the vacuum tube era to today's integrated microcircuits which can handle only minute quantities of voltage current, its sus- ceptibility to EMP has increased significantly. Consequently, this results in modern communications and electronics equipment being highly vulnerable to the power surges of EMP. The significance of these power surges is demonstrated when comparing EMP with lightning. Both involve a sudden pulse of energy and both are attracted to intentional or unintentional collectors or antennas. However, EMP and lightning differ in four crucial ways: (1) EMP pulses much more rapidly. Pulse time for EMP maybe a few billionths of a second; the comparable interval for lightning pulse involves millionths of seconds (8:A-2). (2) Each field strength can differ radically. Lightning maybe a few thousand volts per meter; EMP can involve 50,000 volts per meter (8:A-2). (3) EMP pulses are of short duration--usually less than a thousandth of a second as opposed to lightning pulses that last hundreds of a milliseconds (8:A-2). (4) Lightning occurs at much lower frequencies and in bands well below the frequencies used by the military communications systems. However, EMP concentrates in some of the bands most frequently used by the military's tactical communications systems (8:A-2). This fact is especially significant when considering EMP's power density of 1,000,000 watts persquare meter versus the typical signal strength of .001 watt per square meter which a radio receiver is designed to accept. Accordingly, since EMP is capable of delivering a signal a billion times stronger than the receiver is designed to accept, one can see the urgency to find solutions to this problem (11:J-3). The system of degradation from EMP results in either a permanent failure of a device or a component or a temporary impair- ment which can deny use of the equipment for a period of time. A burned-out transistor exemplifies the former; while a change in the state of a switch represents the latter. Most susceptible to EMP are those components with low voltage and current requirements such as solid state devices, integrated circuits, semi conductor devices, digital computers, digital circuitry, alarm systems and electronic sensors. Generally, as the size of the device decreases, its ability to absorb voltage and current decreases, which results in increased susceptibility to EMP. Vacuum-tube equipment, inductors, tube transmitters and receivers, low current relays and switches are less susceptible. Equipment designed for high voltage use such as motors, transformers, radars, relays, lamps and circuit breakers are not susceptible (2:118). Another necessary variable to consider is the collection of EMP energy. Collectors may be cables, wires, antennas, pipe, conduit, metal structures, railroad tracks - anything that acts as an electrical conductor (8:5-4-5-8). The amount of EMP energy collected depends on the electrical properties, size, and shape of the material comprising the collector. EMP energy may be transferred from the collector to the equipment directly by a physical connection or indirectly through induction (8:5-8-5-10). A vast array of collectors form a huge grid over the entire United States. Its power cables, telephone lines, towers, antennas and railroad tracks have the capability of collecting EMP energy and transferring it to anything physically or electronically connected to them. Thus, for example, any electronic device attached to a telephone line or power line has the capability of receiving large amounts of EMP (8:5-6-5-7). Technology has sought remedies for the effects of EMP since the early sixties. The interest resulted from increased scientific awareness and advances in electronic technology. Not to be stymied by the 1963 partial test ban treaty, United States' scientists forged ahead by building devices which simulate EMP. The Air Force built an EMP testing facility called TRESTLE in 1980 at Kirkland Air Force Base, New Mexico. This device tests the vulnerability of all our new aircraft to EMP (2:119). The Navy's EMP testing facility called EMPRESS I is at Point Patience on the Patuxent River in Maryland. This device can only test frigates and small destroyers to the vulnerability of EMP. However, the navy was not satisfied with the limitations of EMPRESS I and is currently building EMPRESS II, which will have the capability to test every ship the navy has in its inventory for EMP (2:121). In addition, the Department of Army's Harry Diamond Laboratories are devoted to the study of EMP, and the Defense Nuclear Agency has several EMP simu- lation facilities. These are just a few of the facilities and means the military and government uses to study ways to neutralize the effects of EMP. Two main processes exist to protect electronic communications systems from the effects of EMP. The first is shielding and the second is acquiring EMP hardened equipment. There are several different approaches to shielding. The first method, volume shielding, is to shield the rooms or facilities in which equipment is located and this creates a large volume in which the electro- magnetic environment is negligible. Local shielding is another method in which equipment cables and electronic boxes are shielded within a room. This provides electromagnetic protection for each piece of shielded equipment. Thus, the EMP induced currents on equipment and cables are diverted away from sensitive components by the cable shields. The shielding protects electromagnetic fields against sensitive electronic equipment, because it reduces voltages that would re-radiate into electronic equipment (9:3-1-3-14). The second process is to receive electronic equipment that is already EMP hardened, and maintain a strict system hardness main- tenance program. The essential elements of system hardness maintenance includes: (1) Configuration management which prevents future system changes from compromising system hardness (9:4-1-4-3). (2) Maintenance, surveillance, test procedures and equipment must be conceived as a part of the system hardening process and must be implemented by the user (9:4-3-4-7). (3) Training ensures that the measures designed into a hardened system are not degraded by uninformed action or inaction (9:4-8). (4) Documentation must be completed in order to achieve success (9:4-9). Although military concern for EMP was initially lacking, sound programs now exist to overcome the EMP threat. Basic guidance is found in Army Regulation 70-60, which requires the establishment of the most appropriate nuclear survivability criteria for each new system, controls the granting of waivers of nuclear survivability requirements, and insures the system survivability programs meet the imposed requirements. This regulation requires specific nuclear survivability criteria be defined during the concept phase of a system's life cycle and that the Outline Development Plan and contract documentation include appropriate considerations of nuclear survivability (6: 1-G-1). The military now has excellent programs for the fielding of EMP survivable equipment. The following provides a brief status of major communications systems that are EMP hardened. The Defense Satellite Communications System (DSCS)III, the Air Force Satellite Communications System (AFSATCOM) and the Navy's Fleet Satellite Communications System (FLTSATCOM) are fully operational. Another satellite system that will come on line in the 1990's will be the Military Strategic Tactical and Relay Satellite (MILSTAR) and all our military communications satellites will be state of the art. The 21 major switching centers of the Automatic voice Network (AUTOVON) are in the process of becoming EMP hardened. The Federal Emergency Management Agency (FEMA)is in the process of hardening all its Emergency Broadcast Systems radio stations. This is a large radio network system consisting of 600 radio stations. The following provides a brief status of major EMP hardened systems in aircraft and weapons. The E-3A Airborne Warning and Control System (AWACS), the E-4B Airborne Command Post, the EC-l35 Airborne Command Post and the National Early Airborne Command Post (NEACP) are EMP hardened or in the process of being EMP hardened to protect the aircraft's electronic equipment. The B-1B bomber, the Peacekeeper Missile (MX), the air-launched cruise missile (ALCM), the ground-launched cruise missile (GLCM) and the sea-launched cruise missile (SLCM) are weapons that were designed from conception to be EMP hardened.* Obviously, the strategic nuclear forces and the strategic command, control and communications systems received the initial EMP hardening emphasis. However, new tactical systems will have EMP hardening and this will offer the combat soldier and Marine a better chance to survive on the battlefield. Two major problem areas concerning the survivability of communications systems from EMP effects remain. First the civilian industry shows no regard for EMP. This is easy to understand since * The author served in a billet for the last three years that allowed him in depth knowledge of EMP hardened communications systems and weapons. EMP hardening adds significantly to the cost of any new system. In the case of an existing system to be retrofitted it would even be greater (3:31-36). EMP would disrupt the vast electronic networks which our major industries depend upon. In addition, public and privately owned radio and television stations would be damaged. The resulting chaos would present a serious threat to the implementation of civil defense plans and recovery efforts. The second problem concerns the lack of EMP hardening in the military's current tactical equipment. While the capability exists to retrofit EMP hardening to this equipment, sufficient funds are not available. This situation leaves the command, control and comm- unications systems of the tactical commander vulnerable to EMP until the new generation of EMP hardened equipment is acquired (11:J-3). The recommendations, which are offered as solutions to the two problems, are based on the assumption that additional money will not be made available to harden all required systems in either the civil sector or the tactical military sector. The first recommen- dation is that FEMA conduct a study of the effects of EMP on the civilian sector and devise appropriate recommendations. This study must consider lead time to "fix the problems, availability of manual backup systems, use of spare equipment to repair damaged systems and finally, how much it will cost the private sector to avoid this potential communications chaos. The second recommendation for the problem requires the military to use unhardened tactical equipment for the next five years. This is derived from a consideration of several important factors. A number of field expedient techniques and planning considerations for the mitigation of EMP are available in various publications and are listed in Appendix A. Some of these considerations are not always practical or feasible, and they are not as effective as factory installed hardening; however, their use will reduce the effects of EMP and increase the likelihood the systems will remain operational. A second factor deals with planning and training. Tactical units do not train in the use of the effects of EMP in garrison or field exercises. This is a result from lack of command emphasis and time constraints units face while in the field. EMP poses a significant threat to unprotected electronics systems. Although the increasing sophistication of microelectronics results in greater susceptibility of modern systems to EMP, current technology exists to neutralize its effects. To this end, the military established a sound EMP system which has resulted in the hardening of the strategic military systems. However, due to insufficient funds being available serious problems exist in the civil and tactical military communications systems. These problems are not insurmountable, and the implementation of the proposed solutions could contribute markedly to reducing the significance of EMP. APPENDIX A FIELD EXPEDIENT EMP MITIGATION TECHNIQUES AND PLANNING CONS IDERAT IONS 1. Develop SOP's to provide for immediate actions to restore comm- unications. In the absence of electronic communications, messenger and pryotechnics can be used (10:3-3). 2. The keys to the maintenance of effective communications are: planning for outages, proper maintenance of equipment, austerity and redundancy (10: 3-3-3-4). 3. Use ultra high frequency (UHF) and super high frequency (SHF) comm- unications equipment in preference to VHF equipment whenever possible (7:4-11). 4. Avoid the use of broadband radios. Radios operating below UHF are particularly sensitive to EMP (7:4-11). 5. Shut down and protect unneeded and redundant radio systems. This will protect all radios that are not essential from the possibility of EMP (7:4-11). 6. When possible, use antennas that have small radiating elements. The smaller the radiating elements, the less susceptible to EMP (7:4-11). 7. Keep cable and wire runs as short as possible. The wire will act as an EMP conductor (7:4-12). 8. Keep cable runs as straight as possible--AVOID LOOPS. Loops will pick up more EMP than straight runs (7:4-12). 9. Keep cables and wire on the ground where practical. Elevating cables and wires will increase the EMP generated voltages and currents (7:4-12). 10. Use shielded twisted pair cables where options in use of cable exist. Twisted pair cables pick up significantly less EMP than unshielded cable (7:4-12). 11. Shielding is effective for EMP. Sensitive communications equipment can be protected from EMP if properly shielded in metal containers (7:4-12). 12. An effective EMP shield requires that all openings be closed with metal covers (7:4-12). 13. Maintain your EMP shields and shelters. Ensure all doors and access panels are kept closed (7:4-12). 14. Electrically bond cable entry panels to the metallic shelters and shields (7:4-13). 15. Keep exterior grounds short and of low impedance (7:4-13). 16. Establish good exterior grounds when possible (7:4-13). 17. Use a common ground for equipment. For large communications systems usually found at regiment and above use a Tree system (7: 4-13). 18. Ensure all antenna guy lines are properly insulated (7:4-15). 19. Avoid the use of commercial sources of power. Commercial power systems are very susceptible to EMP (7:-15). 20. Keep a supply of critical spares (7:4-15). BIBLIOGRAPHY 1. Clarke, George Major, U.S.A. Interview 2 February 1988. Maj. Clarke formerly served with D.N.A. and D.I.A. 2. Guida, Richard A. Lt. Commander, USNR, "Nuclear Survivability" U.S. Naval Proceeding, December 1985, pp. 116-121. 3. Rudie, Norman J., Dr. "Electromagnetic Pulse Effects and System Hardening: Response of a System." Defense Science and Electronics, June 1986, pp. 31-36. 4. Rudie, Norman J., Dr. "Electromagnetic Pulse Generation and Coupling to Systems: A New Arena." Defense Science and Electronics, May 1986, pp. 72-75. 5. Rudie, Norman J., Dr. "Radiation Effects: SGEMP Phenomena." Defense Science and Electronics, July 1986, pp.75-76. 6. Army Regulation 70-60. "Research, Development, and Acquisition- Nuclear Survivability of Army Material." Headquarters, Depart- ment of the Army, Washington, D.C. 1 October 1984. pp. 1-G-1. 7. Field Circular (FC)50-15. "Nuclear Weapons Effects Mitigation Techniques." Fort Leavenworth, Kansas. 1 March 1984. pp. 4-9- 4-15. 8. Field Circular (FC)50-16. "Electromagnetic Pulse Mitigation Techniques." Fort Leavenworth, Kansas. 1 February 1984. A-2; 5-4-5-10. 9. Field Circular (FC)50-17. "A technical Overview to Electro- magnetic Pulse." Fort Leavenworth, Kansas. 1 June 1986. pp. 1-1-1-20;3-1-3-14;4-1-4-9. 10. Field Circular (FC)50-20. "Nuclear Considerations for Operations on the Airland Battlefield." Fort Leavenworth, Kansas. 1 February 1984. pp. 3-1-3-5. 11. Field Manual 24-18. "Tactical Single Channel Radio Communications Techniques." Headquarters, Department of the Army, Washington, D.C. 30 September 1987. pp. J-1-J-4. 12. Field Manual 100-2-1. "The Soviet Army - Operations and Tactics." Headquarters, Department of the Army, Washington, D.C. 16 July 1984. pp. 2-6-2-8. 13. Field Manual 100-2-2. "The Soviet Army - Specialized Warfare and Rear Area Support." Headquarters, Department of the Army, Washington, D.C. 16 July 1984. pp. 5-2-5-4.
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