The Clinton administration is promoting a limited land‐based system consisting of space‐based sensors, new ground‐based radars (and upgrades to older ones), and 20 to 250 ground‐based interceptor missiles located at one or two sites. Those missiles are designed to defeat a limited attack (tens of warheads) by colliding with oncoming missiles as they are “coasting” in the upper atmosphere along predictable trajectories.
By contrast, some NMD supporters advocate a sea‐based approach that they say can be deployed more quickly and inexpensively than Clinton’s system. The Heritage Foundation, for example, argues that “an affordable and effective missile defense system could become operational within four years and cost less than $8 billion” by installing sea‐based NMD on existing Aegis ships, thereby avoiding the construction costs for interceptors and radars that land‐based NMD would impose.
The problem with this strategy is that interceptors small enough to fit the existing Aegis launch tubes are too slow to catch and destroy ICBMs in their “boost phase,” which is the supposed advantage of a sea‐based system. As a result, entirely new interceptor missiles and launch tubes would have to be designed at significant cost and delay, and even those are problematic because it is doubtful Aegis ships will ever be able to accommodate large‐enough missiles. According to Owen Cote, a national security specialist at the Massachusetts Institute of Technology, “You cannot build a big enough boost‐phase interceptor … and put it on surface ships.”
But let’s say, for the sake of argument, that none of the above was a problem — that Aegis ships could be quickly and cheaply outfitted with intercept missiles of sufficient speed to destroy enemy ICBMs. Would sea‐based NMD then become a good idea?
The answer is still no. Sea‐based NMD requires that Aegis ships be positioned near the launch areas of potential enemies, with the number of ships depending on the number of potential threat nations. But if some Aegis ships are dedicated exclusively to NMD — four to seven is a typical deployment estimate, with at least as many additional ships required for on‐station rotation — then they will not be available for the missions to which they are now dedicated. Making up that shortfall would force the Navy to acquire new Aegis ships at a construction cost of $1 billion each and an operational cost of $20 million per year per ship. This undermines the claim of sea‐based NMD proponents that their system is less expensive because it employs already‐existing hardware.
Sea‐based NMD has deployment limitations as well. Because Aegis ships need to be close to the enemy’s shoreline to be effective, they would be easy targets for sea, air and cruise‐missile attacks. If those ships cannot protect themselves, additional assets would be needed to defend them, further adding to the cost of sea‐based NMD.
Then there are the potential diplomatic problems. Given the relatively short time window during which a boost‐phase intercept is possible, a commander aboard an Aegis ship would need to react immediately to an enemy launch. But what if the missile posed no threat to the United States? It is very difficult to know the ultimate destination of a missile during the early stage of its flight, which means sea‐based NMD could end up destroying missiles launched for scientific or commercial purposes. By contrast, land‐based NMD allows sufficient time to determine a launched missile’s trajectory, preventing the possibility of a mistaken — and provocative — intercept.
The final major problem with sea‐based NMD is that for all its praise as a thrifty alternative, many proponents envision it as the first step toward building a much larger and more expensive global missile defense system designed to defend more than just the United States.
Although it may seem strange to be praising a Clinton administration initiative as cost effective, ground‐based missile defense is farther along in development and is undergoing actual testing. Sea‐based NMD is still only a concept on paper.