The Challenges of Missile Defense

An SM-3 anti-ballistic missile launch from a Ticonderoga-class cruiser. Ship's bell is visible in background.

An SM-3 anti-ballistic missile launch from a Ticonderoga-class cruiser. Ship’s bell is visible in background.

As discussed in a previous post, The Missile Threat, countering missiles is uniquely challenging for militaries around the world. Cheap, readily available, and effective, missiles can allow a smaller force to inflict serious damage on a more capable adversary.

This article elaborates upon the difficulties of countering two types: ballistic missiles and cruise missiles, both of which are offensive anti-surface missiles.

Brief Description of Ballistic and Cruise Missiles

Ballistic missiles follow a ballistic flight trajectory, traveling rapidly upwards and then falling back to earth. They are generally only guided for a brief period after launch and use rocket engines. For a rocket engine, the fuel and an oxidizer are both supplied, whereas a jet engine uses atmospheric air instead of carrying oxidizer. There are many different types of ballistic missiles, such as tactical ballistic missiles (whose ranges are relatively short, generally less than 200 miles) and intercontinental ballistic missiles (ICBMs), which can strike at targets in excess of 3,400 miles. Characteristics of ballistic missiles include relative complexity, large size, long range, and difficulty of interception (a ballistic missile warhead generally approaches in terminal phase at hypersonic speeds, sometimes in excess of Mach 20).

The trajectory of a Minuteman III ICBM with MIRV payload. Note how the missile first ascends, then the payload is pulled back to earth by gravity.

The trajectory of a Minuteman III ICBM with a MIRV payload. Note how the missile first ascends, then the payload is pulled back to earth by gravity. For the original image with labeled stages, see the Wikipedia article on ballistic missiles.

Ballistic missiles first found wide-scale use in World War II, when Nazi Germany developed the V-2 rocket, the first long-range guided ballistic missile. While an impressive feat of engineering, the V-2s were never enormously successful (more were killed producing the weapons than by the weapons themselves). Later iterations, however, would remedy many of the problems faced by the V-2. The V-2’s designers were taken into custody by the US and USSR, and the missile race had begun. Ballistic missiles became some of the most effective and fearsome weapons ever deployed, exceedingly difficult to intercept and capable of destroying the world many times over when armed with nuclear warheads. In fact, the change brought about by the nuclear-armed ICBM can hardly be overstated: never before in human history has the assured ability to obliterate one’s adversary been a couple keys and launch codes away.

Ballistic missiles are so destructive that their overall utility has been generally restricted to deterrence, with one exception: tactical ballistic missiles (also referred to as theater ballistic missiles). The widely exported SCUD, in particular, has been deployed in a multitude of conflicts, where its large warhead and hypersonic impact speed can devastate morale on the receiving end. Despite their size, such missiles can also be elusive: in the First Gulf War, the road-mobile Iraqi SCUDs proved their survivability by largely evading the USAF.

Cruise missiles also present a formidable threat to targets on land and at sea, although for different reasons. As opposed to ballistic missiles, cruise missiles have a relatively flat trajectory and generate aerodynamic lift as opposed to soaring upwards and falling back to earth. Cruise missiles make use of air-breathing jet engines, eliminating the need to carry oxidizer. While this mode of propulsion makes them slower, cruise missiles can be guided throughout their flight path, allowing them to combine range and accuracy.

The flight path of a cruise missile. Note that, instead of travelling upwards and falling back to earth, a cruise missile actually navigates along a pre-determined path.

For example: the advanced US ATACMS ballistic missile has a circular error probable (CEP) of 10-50M, according to Missile Threat. However, this tactical ballistic missile can only travel about 190 miles. The Tomahawk Block IV cruise missile has a CEP of around 10M and can also travel over 1000 miles. Evidently, two systems have similar accuracy, but the Tomahawk has much longer reach. This combination of accuracy, low cost and long range makes cruise missiles ideal for attacking hardened and well-defended targets from a safe distance; losing a $1,000,000 cruise missile to anti-aircraft fire is preferable to losing a $50,000,000 combat aircraft and its pilot.

While ballistic missiles rely on their velocity for survivability, cruise missiles often rely on stealth and saturation attacks to penetrate defenses. Many cruise missiles also utilize a terrain-hugging flight path. When air-defense radar waves are emitted towards terrain or body of water, they will be reflected back to the antennae, producing a “clutter” of false-positives. Cruise missiles take advantage of the clutter by flying close to terrain so as to blend in. Similarly, cruise missiles used against ships (ASCMs) often have a sea-skimming flight pattern which makes them difficult to discern from the surface of the water. Countering such cruise missiles requires a modern and powerful radar which can discriminate between the rapidly moving cruise missile and the clutter of the earth and sea. In addition, countering cruise missiles requires a dense air defense network with ample coverage: a few excellent radars are not of much utility if there is a hill between them and the missile’s flight path. Exacerbating the issue, many cruise missiles can even be programmed to avoid air defense installations.


Evidently, intercepting ballistic missiles and cruise missiles are unique challenges. With regards to the rapidly moving ballistic missiles, interceptors must be designed with the utmost attention to detail and precision. Hitting an object moving many times the speed of sound with another object moving many times the speed of sound is no small feat, and even the smallest of flaws can result in a total failure of the system; for example, a US Patriot missile battery failed to intercept Iraqi SCUDs during Desert Storm as the result of a minuscule clock rounding error. Considering the advanced guidance and manufacturing techniques required to produce anti-ballistic missile systems, it is no wonder that effective ballistic missile defense has taken so long to develop.

Another problem associated with ballistic missile defense is that of the cost-imposition curve. Essentially, fielding ballistic missile defenses is often more expensive than fielding ballistic missiles themselves, leading to an unfavorable situation for the defender. The US GMD program, for example, will cost US taxpayers in excess of $40bn through FY17 (and this $40bn figure is likely below the true costs of fielding the system). This has yielded a few dozen interceptors, the effectiveness of which is not entirely clear. Meanwhile, Russia and other nuclear-armed nations have hundreds (or thousands) of nuclear missiles; the cost of procuring and maintaining a few dozen ICBMs is nothing near $40bn for a nation like Russia or China. Of course, R&D costs account for a significant portion of the $40bn figure, but that is exactly the point: developing a brand-new and hugely expensive weapons system to counter a decades-old threat is far from being on the right side of the cost-imposition curve. This is a perpetual problem for missile defense: ballistic missile defense technology is fledgling and cutting edge, while the ballistic missiles it struggles to counter are relatively low-risk and cheap. In some arenas, this gap is being closed. Some smaller ballistic missile interceptors such as the Patriot PAC-3 are indeed cheaper than some of of the missiles they intercept. Of course, the capabilities of point-defense interceptors such as the PAC-3 are relatively lackluster, as they can only defend a small area against relatively low-performance ballistic missiles.

Cruise missiles also pose a unique threat. Already mentioned are the requirements for modern radars and interceptors, but that is far from the whole story. Volume of interceptors is a significant issue as well, because of the aforementioned low-cost and high-accuracy characteristics of these missiles. For example, a US guided missile destroyer operating in the South China Sea may expect to have tens if not hundreds of cruise missiles employed against it in a conflict. However, these destroyers are limited in the interceptors they can carry, of which multiple may be required to eliminate each oncoming cruise missile. In some cases, cruise missiles can overwhelm an adversary by sheer numbers: it simply is not realistic to equip every ship and base with enough interceptors to repel a cruise missile saturation attack. The cost-imposition curve is also notable here as well, because many interceptor missiles are more expensive than the relatively cheap cruise missiles they eliminate. Similarly to in ballistic missile defense, the employment of smaller and cheaper interceptors can partially remediate this problem. For example, four Evolved Sea Sparrow Missiles (ESSMs) can be fit into a cell normally reserved for one SM-2 or SM-6, allowing for a much higher volume of interceptor missiles to be carried. But again, there are limitations. For one, the ESSMs have far shorter range and a lighter payload than the SM-2s and SM-6s they supplant.

Clearly, both cruise missiles and ballistic missiles pose interception challenges. However, there are innovative ways in which the devastating effects of these missiles can be reduced. A future post will cover the ways in which militaries of the world seek to counter ballistic and cruise missiles to turn the tables in favor of missile defense.

Some reading:

Interesting information about cost-imposition.

This superb blog has many insights into US ballistic missile defense.

About the Author

Alex Hempel
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