Scientific advances have provided extraordinary new capabilities for mankind to use for good or ill. Yet even the most magical of new technologies is constrained by the nature of matter, the laws of physics and the universal constants. Weapon systems have been a focus for much research and development effort. Each new offensive capability has spawned a search for an effective defensive countermeasure. The early advocates of air power believed that "the bomber will always get through". Radar, fighters, guns and missiles were developed to prove the early theorists wrong. Against such defences, the bombers' success rate had to be improved by flying lower, or using electronic counter-measures, or by giving them a smaller radar cross-section. At any given time in the past 60 years, there has been a technological battle between offence and defence in air combat capabilities. The trend has been increasingly in favour of offensive capability with the move towards greater use of ballistic and cruise missiles. The effectiveness of offensive weapons have also increased with improvements in precision of attacks. Finally, the advent of weapons of mass destruction (WMD) have made the requirement for absolute assurance in any defensive system much more demanding.
Systems that attempt to defend against incoming offensive missiles have therefore to be seen, from a military perspective, as but one aspect of a complex interplay of offensive and defensive capabilities. Airmen argue over whether air supremacy is achieved more efficiently by an offensive counter-air campaign (targeting airfields, command centres, missile sites and aircraft in their bunkers), or by air-to-air fighters patrolling the skies. Both are needed, but long term investment decisions need to make judgements about the relative priority of each campaign. Resources are finite for every country, and in most countries those funds available for the military are declining. Any military benefit analysis of missile defence must weigh its relative contribution against other capabilities foregone to free up sufficient funds.
No defensive system can give 100% assurance of preventing a successful offensive attack. There are many factors which affect the overall success rate of defences. The theoretical technical capability of a given defensive system will be modified in any given scenario by the numbers of attacking systems, the number of defending systems, the redundancy of the defences, the reliability of hardware and software, the warning and reaction times, the deviation of the attack parameters from the optimum assumptions, and also by less predictable human factors. Higher assurance is bought at extra cost through such approaches as layered defences, duplicated systems and automated response. A judgement has to be made about the acceptable rate of defensive leakage for any given scenario.
In looking for a military judgement on investment in missile defensive systems, we must examine the range of possible scenarios. These can be broken down into four broad requirements starting with the most difficult:
- 1. Territorial defence against a major WMD attack.
- 2. Territorial defence against a very limited WMD attack.
- 3. Defence of operational military formations against missile attack.
- 4. Point defence of key locations against missile attack.
The threat of a major WMD attack is the most serious challenge that any government faces. Throughout the Cold War, it was the focus of all strategic thinking. The prevention of such an attack was achieved through nuclear deterrence, which required NATO and the Warsaw Pact to field credible second strike forces which could survive a nuclear attack. In the 1960's, the US and the Soviet Union each did a considerable amount of work on developing anti-ballistic missile (ABM) defensive systems to reduce the threat to their territories posed by each other's nuclear tipped missiles. It rapidly became clear to both that the cost of improving the offensive systems to counter ABM defences was considerably less than the cost of the ABM system. In March 1969, President Nixon announced that defence against a heavy Soviet attack was not feasible. The realisation by both sides that Ballistic Missile Defence (BMD) was impractical, unaffordable and would lead to increased offensive deployments by the opposition led to the ABM treaty in 1972.
Not surprisingly, there remained a strong body of opinion that technology must be able to provide some form of defence against the nuclear threat. This was voiced by President Reagan in his speech to the nation of 23 March 1983 when he said: "What if .... we could intercept and destroy ballistic missiles before they reached our own soil or that of our allies?". The Strategic Defense Initiative (SDI) was launched with the aim of finding an answer to the President's vision. The proponents of SDI argued that space, computer and weapons technology had advanced considerable since the earlier attempts to develop BMD. Yet technology had also moved on in offensive nuclear capability. Small multiple warheads coupled with decoys allowed many more threats to be posed to any defensive system by each hostile missile. While the proposed layered system might give a much greater assurance of successful interception, an optimistic projected defensive leakage rate of just 1% still represented 100 nuclear warheads arriving from the 10,000 that the Soviets had available at the time. A vastly expensive, technically unproven, potentially destabilising SDI deployment would not provide useful protection to US major centres of population. Again, much research money was spent and much strategic debate was had before the SDI quietly disappeared with the end of the Cold War.
While the threat of a large scale nuclear attack on any nation is now much reduced, there are still a large number of nuclear weapons and long-range delivery systems available to the USA, Russia, China, France and the UK. Nevertheless, the technological infeasibilty of 100% effective missile defences remains a strong argument against investing funds to try to defend populations from a mass WMD attack, particularly as the threat of such an attack is very low. This view appears to have been accepted in the United States and elsewhere. However, the technology advances explored during the SDI programme have left an enthusiasm for deploying a defensive system against a more limited WMD threat.
When it became clear in the 1960's that the US would not be able to deploy a useful ABM system to defend its population against a nuclear exchange with the Soviet Union, the deployment of a light system was justified on the ground of protection against a limited attack. That attack was either from a power with few weapons (China at the time) or an accidental Soviet launch. In the event, the US dismantled its only deployment and the Soviet Union maintained only its single treaty permitted site around Moscow. The defensive technologies researched during the SDI period of the 1980's are now in a similar fashion seen as providing the technical feasibility for a defence against a limited WMD attack on a nationwide basis: National Missile Defence (NMD). In this case, the argument is made that a greater than 99% assurance of interception will provide adequate capability against a threat from a "rogue state" proliferator, who might acquire a small number of long range missiles with which to threaten the United States. Although technical development of such systems is still proving elusive and expensive, it is not unreasonable to assume that, given sufficient time and money, a multilayered NMD system with such limited aims may be possible in the relatively near term.
The scenario requires future circumstances in which the United States perceives itself to be under threat of nuclear, biological or chemical ballistic missile attack from one of a handful of states, which might include Iran, Iraq and North Korea. To counter such a threat would require the deployment of a wide area layered defensive system, which in turn requires a radical renegotiation of the ABM Treaty. Assuming that such a system were deployed, what would be the effect on the strategy of potential enemies? There would be an incentive to increase missile numbers and warheads to achieve a greater likelihood of penetration. Perhaps more productively, alternative delivery means would be fielded. Options include commercial aircraft, cruise missiles, small drones, container ships or human agents. All of these alternative systems could be effective biological weapon carriers, and some would allow nuclear weapon delivery. Thus an NMD deployment would only provide partial protection against a limited threat from a small number of states. It would not give sufficient confidence in the United States' invulnerability to allow it to ignore the threat from potential proliferators, nor would it protect against the non-state actors with non-ballistic missile WMD capability.
Deployment of NMD would also affect relations with other nuclear powers, and with Allies. Other nuclear powers would have a disincentive to reduce their own holdings of weapons in a world where excess numbers may begin to have significance again. This in turn increases the risk of accidents and reduces overall security. The US has strategic alliances in Europe, Japan and Korea. The way in which these arrangements of shared risk would be affected by the deployment of a US NMD system is not clear, but there are already signs of discomfort in terms of alliance relationships, which bode ill for global security.
An NMD system would be very costly to develop, to deploy and to maintain. Given the military capability needs shown in such operations as Kosovo, it is unlikely that diverting scarce resources into NMD would be a sensible military priority.
Operational military formations will regularly find themselves threatened by attack from enemy systems. Increasingly, such threats may be from surface to surface missiles as well as artillery and enemy aircraft. While nuclear attack remains improbable (and is deterred by the possibility of nuclear retaliation), there is a real threat of chemical agents being used by some potential enemies. The Gulf War of 1991 was a good example of a campaign where allied troops had to be prepared to be attacked by Iraqi Scud missiles with the possibility of chemical warheads. Such a threat means that troops will be forced to operate in NBC protective clothing and take other protective measures. This reduces operational capability significantly, even if chemical attacks do not take place. Nevertheless, such a threat is only one of a number of concerns that a deployed force will have. The main weight of fire is likely to be carried out by aircraft dropping conventional bombs.
In the Gulf War, the deployment of Patriot missiles to provide some limited anti-Scud intercept capability was seen as politically important. From a military effectiveness aspect, their role was more a boost to troop and civilian (particularly in Israel) morale than a change to the balance of forces. Troops still needed to take NBC precautions and to defend against the whole spectrum of potential threats. A more effective counter to the Scud threat was to carry out offensive missions to destroy the launchers and the missiles. Undoubtedly, it will be possible to continue to improve the anti-missile effectiveness of Patriot like defensive systems. This will be a sensible strategy for improving air defences for operations.
Proposals for a more comprehensive deployable theatre wide defensive system begin to run into cost effectiveness problems. To provide a layered defensive system over the theatre of operations would require many of the elements of the NMD system. However, the system would have the added complication of having to be deployable worldwide. It could be more austere (fewer layers) because a higher leakage rate would be acceptable. In the end there will have to be an analysis of the trade-off between cost and complexity. It is unlikely that even the most costly solution would provide sufficient defensive assurance to allow NBC passive defence measures to be abandoned. Given this, it would seem unlikely that comprehensive layered theatre missile defence systems will be a sensible investment from a military point of view.
The easiest requirement for defence against missile attack is that of protecting a discretely located small area. The best example is that of a naval ship. The target is well defined and all defences can be optimised to counter only those incoming missiles which will hit the ship. Already there are ship borne missile defences which achieve high degrees of protection. Similarly, aircraft routinely defend themselves against missile attack. There is a need to provide this type of protection for key communication nodes, headquarters and other installations. The smaller the location, the easier it is to provide late interception or deflect the incoming missile from its target. The development of low cost point defence systems would allow them to be more widely deployed than the limited numbers of such systems available currently, and would begin to give some wider area protection. Concentration on this aspect of missile defences would cause no treaty problems, would improve military capability in all aspects and is technically low risk.
From a military planner's point of view, there would seem to be benefit in directing research and development effort into the incremental improvement of ground-based point defence anti-missile systems. Multi-layered wide area missile defences will distort defence spending and are unlikely to provide significant improvements in useful military capability.