A new report by the Cato Institute says that plans to base interceptors on ships to defend against intercontinental missiles won't work. While the Navy Theater Wide system could defend regional targets against theater missiles, engaging ICBMs in the boost phase is a very different thing. Space-based sensors would have to tell the ships when to fire, and a new long-range interceptor would have to be designed. Worse, this new interceptor would not fit into the existing vertical launch cells, which were not expected to mount a missile of such long range. The Cato Institute study says it would cost ten times as much to provide ship-based systems to protect the US as it would to build similar systems on land.--Stephen V Cole