The Nuclear Threat Initiative website offers an assessment inAddressing the Spread of Cruise Missiles and Unmanned Air Vehicles (UAVs)(from March 2004):
America's adversaries are bound to draw important lessons from the performance of U.S. missile defenses against Iraq. Referring to Iraq's use of cruise missiles, the chief-of-staff of the 32nd Army Air and Missile Defense Command told the New York Times "this was a glimpse of future threats. It is a poor man's air force. A thinking enemy will use uncommon means such as cruise missiles and unmanned aerial vehicles on multiple fronts." At least two reasons account for why we should anticipate an acceleration of interest in acquiring cruise missiles and UAVs. First, countries wishing to deter U.S. military interventions were unlikely to invest heavily in cruise missiles until American missile defenses performed decisively better against ballistic missiles than they did during the 1991 Gulf War. Patriot's success against Iraq ballistic missiles in 2003 coupled with problems coping with cruise missile attacks increases the incentive to acquire difficult-to-defend against cruise missiles and UAVs. Second, America's adversaries are likely to appreciate the operational advantages of combining ballistic and cruise missiles launches to maximize the probability of penetrating even the best American missile defenses. Converting small airplanes or UAVs into weapons carrying "missiles" offers a particularly attractive poor man's option. When these, in large numbers, are combined with more expensive and sophisticated ballistic and cruise missiles, they raise the stakes enormously for American missile defenses. Consider, for example, the dire and unfavorable cost-exchange arithmetic associated with current U.S. missile defenses and conceivable adversary missile threats. The guidance upgrade alone on the PAC-2 Guidance Enhanced Missile costs $400,000 per missile, and each new PAC-3 interceptor costs $3.5 million. A flock of cruise missiles or converted airplanes several orders of magnitude cheaper could readily saturate most economically feasible missile defense architectures. Thus, controlling the quantitative spread of cruise missiles and UAVs through improved nonproliferation policies is an absolute necessity to guarantee confidence in our missile defense expenditures.
Saturation with cheap cruise missiles or UAVs is of less concern when we consider terrorist use of such systems against the U.S. homeland. Were an attack to involve delivery of a weapon of mass destruction, one successful strike against the American homeland—particularly a major urban target—could have devastating consequences. Due to its aerodynamic stability and capacity to release agent along a line of contamination, a cruise missile or UAV is much effective than a ballistic missile in delivering chemical or biological payloads (conservatively enlarging the lethal area for biological attacks by at least 10 times).
Cruise missiles or UAVs might be launched from concealed locations at modest distances from their targets, or brought within range and launched from freighters or commercial container ships—in effect, a "two stage" form of delivery. Al Qaeda is believed to possess at least 15 freighters. In the aftermath of the September 11, 2001 terrorist attacks, key U.S. decisionmakers began to take such two-stage threats more seriously. The 2002 National Intelligence Estimate (NIE) on the ballistic missile threat to the United States drew attention to the covert conversion of a commercial container ship as a launching pad for a cruise missile. Even a large, bulky cruise missile like the ones Iraq used to fire at coalition forces last year could be equipped with a small internal erector for launching and still fit comfortably in a standard 12-meter shipping container. Indeed, the 2002 NIE argues that because such a delivery system, among several others, is less costly, easier to acquire, and more reliable than an intercontinental ballistic missile, a cruise missile attack against the American homeland is more likely to occur than a ballistic missile attack.
Making matters worse from a missile defense standpoint, a terrorist group might wish to convert a small kit airplane into an autonomous delivery system, which could be launched from locations near their intended target. The development approach would be similar to a state wishing to create a poor man's air force of cruise missiles. Larger than the ultralights used by Iraq last year, kit airplanes could be converted at substantially less cost, with less significant engineering prowess, and fewer steps—and thus less chance of failure—than either converting anti-ship cruise missiles, as Iraq did, or small reconnaissance or target drones, into land-attack systems. From a worldwide list of manufacturers, a terrorist group could choose from among nearly 500 well-tested designs, many with ranges exceeding 600 miles, payloads of 400 pounds, football-field takeoff distances from soft, grassy areas, and stall speeds of under 80 knots. Such slow speeds actually furnish an advantage as many of our sophisticated lookdown airborne and ground-based air defense radars eliminate slow-moving target on or near the ground to prevent their data processing and display systems from becoming overtaxed. This means that propeller-driven kit airplanes flying under 80 knots per hour would be ignored as potential targets...
The US Navy is looking at a solution in its Standard Missile system:
While much attention has been focused on ballistic-missile defense, the Navy has always been concerned with cruise missiles, which fly below radar, hugging the terrain or the ocean surface. The Navy faces a threat from land-attack cruise missiles as well as antiship missiles.
“That is why they are pursuing a weapon that can handle both,” Zaloga said.
That weapon is the Standard Missile-6 (SM-6) extended-range active missile, or ERAM.
For use as an anti-air warfare and area air-defense missile, the SM-6 is expected to provide extended-range anti-air warfare capability against a multitude of targets, including aircraft, unmanned aerial vehicles and land-attack and antiship cruise missiles in flight, either over sea or land.
With its active radar system, the SM-6 also is expected to engage over-the-horizon targets using a future networked fire-control data system for targeting.
The SM-6 is designed to replace the Navy’s Standard Missile-2 (SM-2) Block IV surface-to-air missile, which was not purchased in large quantities because it was to be replaced by the SM-2 Block IVA that was to have anti-air warfare and theater ballistic-missile defense capability.