It has now been two decades since the U.S. Navy formally adopted the ballistic missile defense mission. For much of that time, ballistic missile defense was a relatively minor role, funded mainly by various incarnations of what is now the Missile Defense Agency. In the last few years it has grown enormously, for two reasons. First, it counters the Chinese anti-carrier ballistic missile. Second, it is now the core of the part of the U.S. national missile defense system erected to cover our allies against theater weapons such as those Iran and North Korea are building.

Basing ballistic missile defense at sea gains the United States enormous advantages, just as basing strike aircraft there does. The missiles, like the strike aircraft, can operate freely without the permission of local governments. Often it turns out, as it did in the 1991 Gulf War, that our ability to operate without permission helps a government that wants protection but has internal problems. If the government cannot veto our help, those who do not want it to be protected see no point in spending their political capital against us. That was very much the case in Saudi Arabia in 1991. Saddam Hussein tried to abort the protection of Saudi Arabia by U.S. forces by charging that no true Muslim could tolerate unbelievers (Americans) on the country’s sacred soil. The Saudi government found it difficult to reply, even though it was aware that Saddam was setting up the country’s destruction. The deployment of U.S. carriers, which the Saudis could hardly veto, settled the issue in favor of protection – and paved the way for the buildup that ejected Saddam from Kuwait.

Basing defensive missiles at sea also buys vital flexibility. The international situation changes continuously. A defensive deployment that is appropriate to one evolving crisis becomes obsolete suddenly, but it is difficult to redeploy assets based ashore, the basing of which entailed considerable political and economic costs. Ships can be moved suddenly, quickly, and at almost no political cost.

Ships at sea are also neutral. In a post-Cold War world, we often find that our friends are each other’s enemies – the obvious case is India and Pakistan. If they began trading missiles, it would be very much in our interest to abort that exchange by shooting down some or all of them. Neither country would be particularly amused by a U.S. demand that it accept land-based systems for that purpose. The India-Pakistan problem is likely to be typical of the post-Cold War world, which is no longer dominated by any kind of polarization. Our freedom to operate is likely to become more and more important.

The naval anti-missile mission began in the last days of the Cold War. As the Soviet threat of mass missile attack against the United States faded, it became clear that the shorter-range weapons many countries were buying were a threat not only to our allies but also to U.S. forces that might be deployed abroad to keep the peace. In effect, the end of the Cold War freed many local powers to pursue their own ambitions. Local wars became more, not less, likely.

The first such war, the fight against Iraq in the Gulf in 1991, graphically demonstrated the new threat. Saddam’s forces fired Scuds into both Saudi Arabia and Israel. The strikes on Saudi Arabia were intended to show the Saudi public that their government could not protect them. Those against Israel were intended to push Israel into the war and thus show that Saddam, not the coalition governments, was the true leader of the Arabs.

Scuds were inaccurate, so it was unlikely that Saddam was trying to deal with specific targets. However, one of the Scud hits carried an important lesson. The missile fell into the water about 1,500 yards from a pier in Jubayl, Saudi Arabia. On the pier were tens of thousands of tons of ammunition. Alongside were both the ships carrying support equipment for the Marine Harriers. This was not one of many piers. In a modern harbor adapted to container shipping, each pier is so efficient that few are needed. Often there is only a single pier. The pier in Jubayl had been, and was still, a key element of the logistical train that ultimately led across the border into Kuwait.

It was unlikely that the usual Scud warhead, even had it hit the pier, would have caused catastrophic damage. However, Saddam had chemical weapons, which he had used in the past. A chemical warhead would have given a Scud, even one missing as this one had, a broad enough footprint to cover the pier.

The message was twofold. First, ballistic missiles fired at fixed targets could be decisive. Without the Jubayl pier, the buildup in Saudi Arabia could not have proceeded. There was no alternative to bringing materiel by sea. Saddam could not have been ejected from Kuwait without the heavy ground force that depended on that link. Moreover, the link had to be maintained, because munitions had to be replaced as they were used – hence the mass of munitions on the pier.

Second, anything fixed in a forward area could no longer be considered secure as long as it was within ballistic missile range. With the end of the Cold War, the U.S. Navy more and more focused on projecting power into unstable areas, and that often meant supporting troops ashore.

All of this was aside from the need to support allies that might find themselves under missile bombardment; the obvious example was South Korea.

In 1990, Congress formally directed what was then the Strategic Defense Initiative Organization (SDIO) to develop a plan to defend allies and forward-based U.S. forces against short-range and theater ballistic missiles. Up to this point, SDIO had concentrated on the national missile defense envisaged by President Ronald Reagan, and that in turn had largely been treated as an outgrowth of the U.S. Army’s lengthy anti-ballistic missile efforts. Now Congress ordered that the Navy and the Air Force be included. That was by no means due to Navy pressure, and indeed the Navy leadership feared that adding the ballistic missile defense mission would detract from other, more urgent, missions in an era of reduced post-Cold War money.

Given the mandate, SDIO paid for a small study to see what the Navy could do. It turned out that the software-controlled SPY-1 radar of the Navy’s Aegis system was adaptable to the new mission. During the Gulf War, Aegis cruisers sometimes detected the early phase of a Scud flight, though they did not track the missile. That was partly because their signals were not designed for very small, distant, fast targets. It was also because the radars used their software to filter out what their operators considered irrelevant targets. When tapes from the ships were analyzed after the war, it became obvious that they had detected the Scuds, and that they had kept detecting them through their flights. With different software, they could have tracked the Scuds and even predicted their impact points.

SDIO was already working on a new kind of ballistic missile interceptor, LEAP (Light Exo-Atmospheric Projectile). LEAP was designed to be fired by a missile at high altitude. It would lock onto an incoming warhead and crash directly into it. LEAP had been conceived as part of a massive system called Brilliant Pebbles, in which hundreds of satellites each would have carried many LEAPs, firing them into the enemy’s cloud of missile warheads. However, LEAP was small enough to fit atop a missile like the Navy’s Standard.

The Scud attack on the Jubayl pier convinced the Navy leadership that the ballistic defense mission was worthwhile. It was obvious that it would be mounted from Aegis ships armed with Standard Missiles. Each ship had a fixed number of vertical launchers. To what extent should their air defense or land attack (using Tomahawk) capacity be turned over to ballistic missile defense?  The Navy adopted a two-tier approach.

Short-range missiles like Scuds could be engaged by a Standard Missile with modified fuzing and an additional infrared (IR) sensor, a missile designated SM-2 Block IVA. It had a big booster that filled the vertical launcher. Probably the most important virtue of this missile was that it could deal not only with Scuds and their ilk but also with the aircraft and anti-ship cruise missiles normally engaged by SM-2. The key change in Block IVA was the additional sensor, which enabled the missile to home on a target not subject to illumination by the Aegis ship. It relied on the fact that a fast warhead would be an excellent IR target.

SM-2 clearly could not deal with longer-range missiles. For that, a defending missile had to reach outside the atmosphere. Whatever the Navy developed had to fit the existing vertical launcher. The choice fell on a Standard Missile with a new upper stage, which in turn would fire a LEAP. Ultimately this missile was designated SM-3.

Key to the entire program was the Aegis system. It was already clear that, because the SPY-1 radar was software-controlled, it could be modified to concentrate on ballistic missiles rather than on airplanes and air-breathing missiles. That was not quite enough; it also needed a more powerful source of radar power. However, the radar was close enough to what was ultimately needed to be very encouraging. What was less obvious was the way in which the Aegis combat system was naturally adaptable to the new ballistic missile defense mission.

The core of Aegis is a tactical picture maintained in the system’s computer, carrying target and defending missile tracks. Based on the way in which the picture evolves, the system commands its interceptors to close in on the targets. Normally in the final stage of interception the system turns on a slaved illuminator, and the missile homes on the radar energy reflected by the target. Clearly no illuminator was powerful enough to guide a LEAP far out in space. However, the system was already designed to tell a missile carrying a LEAP where to go so that the LEAP itself could complete the interception. To make that work, the system had to know just where the interceptor was, more precisely than the SPY-1 far below could say. SM-3 therefore needed GPS. The entire project was simplified by the fact that SM-3 was based on the existing and well-understood SM-2 missile, rather than on some entirely new one. From the point of view of SDIO, the Navy project was attractive because Aegis had been designed to accept track information from external sources, a capability enlarged as the Navy developed the Cooperative Engagement Capability (CEC) for enhanced fleet air defense. Thus Aegis ships could naturally accept and use cueing information from sensors such as the projected system of missile warning satellites.

The modified SM-2 was associated with the Navy Area Defense System, and SM-3 with the Navy Theater Wide (NTW) system. Existing SM-2 Block IV missiles were converted into Block IVAs, and the limited Navy system became operational, the ships (with modified radars) being designated “Linebackers.” However, planned production of new Block IVA missiles was cancelled in 2001 due to the rising cost of the missile. That cancellation may have reflected a higher-level preference for the Navy and the Army to standardize on their lower-tier defensive weapon. Such standardization was impossible for the Navy because it would have eliminated the ships’ ability to deal with other existing threats.

The SM-3 program survived. The first Navy LEAP flights were aboard modified SM-2 (ER) missiles, which had 13-inch boosters rather than the 21-inch boosters envisaged for SM-3. These flights in effect proved that the SM-3 concept was viable. Development proved somewhat more difficult than had been expected, but it was entirely successful. The Navy envisaged a modest force of five SM-3 ships and 80 missiles on station. Because SM-3 fit existing launch cells, and because the necessary changes to the radar and the combat system were limited (largely to new software), this force could easily be expanded to meet any change in the threat. Ultimately any Aegis ship could be modified so that it could function both in the usual fleet air defense mode and in the anti-ballistic missile mode. Thus the Navy’s growing force of Aegis ships represented an enormous potential capacity that could quickly be realized.

SM-3 could deal with an intermediate-range ballistic missile, but not with the intercontinental-range missiles any U.S. national missile defense system would face (the United States began to erect a national missile defense after the George W. Bush administration withdrew from the ABM Treaty in 2003). To do that it needed a much more energetic booster and a more powerful radar (the target missile flies higher and faster). A naval element in a national system offers considerable leverage, because an enemy cannot be sure of where the interceptors are. That had been obvious in past attempts to build a national missile defense, in the 1960s. A longer-range missile would also be able to deal with an intermediate-range target at much greater range, offering more shots per target. About 2000, the Navy considered a future project for a missile cruiser it called CG(X), which would have a new, more powerful radar and which would presumably have accommodated the larger launch cells needed for a more powerful booster. This project lapsed.

SM-3 became much more important, however, as it became obvious that the ballistic missile threat to the fleet was expanding.

Whether or not the Chinese “carrier-killing” missile works as advertised, the U.S. Navy must demonstrate that it can handle this new threat. Otherwise, allies in the Far East who rely on our ability to use sea power to reinforce them will feel naked, and our position with some of our most important trading partners will begin to unravel.

There was a reason that the need for ballistic missile defense was cited to justify cancellation of the DDG-1000 program (oriented entirely toward land attack) in favor of continued construction of Aegis destroyers.

SM-3 made its first successful test flight on Sept. 24, 1999, and on Jan. 25, 2002, it successfully intercepted a ballistic missile target in the fourth of nine developmental flights. On Dec. 17, 2002, President George W. Bush formally approved deployment of the Aegis BMD system in 2004. Simultaneous anti-missile and anti-air engagements were demonstrated on April 26, 2007.

The Aegis system is well-adapted to accept data from outside a ship, because the tactical picture around which it is built need not take the data from the ship’s own SPY-1 radar. That has been clear for some time, since Aegis ships can exchange data at the level of radar plots (individual target detections) through the CEC. An Aegis BMD ship demonstrated its ability to launch a missile on the basis of remotely-obtained data in 2006, and it showed the same ability using BMD sensors in 2008. The current plan is to demonstrate an engagement entirely using remote data some time after 2015. Engagement using remote data becomes particularly important when Aegis ships are integrated into a larger regional defense plan, as in NATO Europe. There, various remote sensors, including a big TPY-2 acquisition radar and, presumably, satellites, will be integrated with both Aegis ships at sea and Aegis land sites. The use of remote sensors extends the system’s detection range and therefore its battle space, giving it more time to track targets and to fire its missiles.

Moreover, on Feb. 20, 2008, Aegis and SM-3 demonstrated what they could do in a real engagement. A 5,000-pound U.S. satellite was tumbling into the atmosphere, out of control. The satellite’s tanks of toxic propellants (normally used to maneuver it in space) were likely to survive re-entry, due to the sheer mass of the satellite. If they fell on land they might well kill people. This was not a new problem; it had been dramatized by the crash of a Soviet radar satellite, which was nuclear-powered, in the 1980s. Two cruisers armed with SM-3 missiles were rapidly modified to deal with the satellite, which was somewhat outside their planned capability. It took one shot from USS Lake Erie to destroy the satellite at an altitude slightly greater than 150 miles, at a closing speed of more than 22,000 mph.

It might be argued that the satellite was an easier target than an incoming missile. It was a lot larger than any warhead. However, it was tumbling unpredictably, whereas a missile warhead flies a much more predictable path.

The first fleet firing (making SM-3 fully operational) came on Nov. 1, 2008.

Allied navies agree with the U.S. Navy that ballistic missile defense is a vital mission. Japan has adopted SM-3, and has also agreed (see below) to participate in the missile development program; Japanese involvement began with a 1999 Memorandum of Understanding. As of late 2010, Japanese ships had fired four SM-3s. Spanish and Dutch ships have participated in U.S. tests of the SM-3 system, the Spanish Méndez Núñez having BMD software added to her Aegis system. Other navies already involved are those of Australia (which is building Aegis ships) and the United Kingdom (which would have to develop an anti-missile version of its own Sea Viper/PAAMS system). South Korea, which is building Aegis ships, has a current operational requirement for a sea-based terminal missile defense system of exactly the type the U.S. Navy and the Japanese Maritime Self-Defense Force currently have. Germany has a liaison officer at the Aegis BMD site.

SM-3 is now also the missile chosen by the United States to help defend NATO in Europe from intermediate-range missile threats, such as that posed by Iran. Initially the plan was to emplace in Poland and in the Czech Republic the same Ground-Based Interceptors (GBIs) as were being deployed in Alaska and in California. In September 2009, however, President Barack Obama announced that instead a phased approach would be adopted, suited not only to Europe but also the Far East. That kind of flexibility was possible because the phased system was based on the existing SM-3 aboard ships – which could immediately begin patrols off southern Europe. Later, SM-3 cells would be built ashore. The only really new element of the European system would be a big transportable phased array radar (TPY-2) intended to acquire targets and then to cue the launchers. Associated with TPY-2 is a new battle management system. Ships are to get a next-generation radar better adapted to detecting and tracking ballistic missiles.

The new approach to defending allies was possible because in the fleet of Aegis ships, much of the required capability already exists. It does not have to be built from scratch. SM-3 already exists. Whatever its future may be, it has already demonstrated considerable performance against realistic targets. Placing the existing missile ashore uses that demonstrated capability.

It also reduces the unit cost of the SM-3 missile by greatly increasing production. That in turn encourages further stepwise improvement, in planned blocks. Blocks are to alternate between improvements in the kill vehicle (descended from LEAP) and in the missile airframe and kinematics, so that they always build on a firm foundation. The current missile is Block IA, built on the body of the SM-2 Block IVA missile plus a new upper-stage motor. Block IB is a new kinetic warhead, to be in service by 2015. Block IIA, being co-developed with Japan under a June 23, 2006, agreement, replaces the existing SM-2 missile body with a 21-inch body, so it fully exploits the available space in the vertical launcher cell (it requires a new lightweight canister). It should be available about 2015. Block IIB (2020) is to use that new full diameter for a new, more capable kinetic warhead.

All of this left the problem of the short-range missile, which was likely to be used in much greater numbers than the more expensive longer-range ballistic missile. There may have been an attempt to revive SM-2 Block IVA in the form of the “black” SM-5 missile, but it died. The Navy is now buying SM-6, which has an active radar seeker in place of the semi-active seekers of past Standard Missiles. That enables it to deal with targets beyond the horizon of the ship’s slaved illuminators, such as overland cruise missiles. However, it probably also provides the capability SM-2 Block IVA would have offered against short-range ballistic missiles. Unlike SM-2 Block IVA, it apparently exploits the ship’s slaved illuminators when fired against airplanes and air-breathing anti-ship missiles.

At one time the idea that the U.S. Navy would have to deal with enemy ballistic missiles must have seemed fanciful. The Soviets deployed such a weapon during the Cold War (it was designated SS-NX-13 by NATO), but in such small numbers that it was irrelevant. There were occasional suggestions that concentrating on the Soviet aerodynamic threat might leave a fatal gap, but it was so difficult for a ballistic missile to hit a moving ship that the idea could be dismissed. Then it became horribly realistic as short-range and then theater ballistic missiles became common in the post-Soviet Third World, exactly the place the U.S. Navy had to project national power. The threat was graphically demonstrated at Jubayl during the Gulf War. The visionaries who recognized both how important the threat was and how well Aegis was adapted to handle it have now been vindicated, both by various regional missile threats and by the emerging Chinese anti-ship ballistic missile threat. Thanks to those visionaries, the U.S. Navy is now in an excellent position to deal with the emerging problem.

*All opinions expressed are the author’s own, and do not necessarily reflect those of any agency with which he has been associated.

This article was first published in Defense: Fall 2011 Edition.