HONOLULU, Hawaii (AP) -- The Navy intercepted and destroyed a warhead as it separated from its booster rocket during a test Thursday off Hawaii -- the first time a ship at sea has shot down a multi-stage missile.The guided-missile cruiser USS Lake Erie fired an interceptor missile and knocked out the rocket's warhead about 100 miles (160 kilometers) above the Pacific, the Missile Defense Agency said in a statement.The achievement is considered significant because medium- and long-range ballistic missiles typically have at least two stages. Intercepting such missiles after they separate is difficult because sensors must be able to distinguish between the body of the missile and the warhead.All previous tests of the sea-based missile defense system involved short-range missiles that stay intact.The military's ground-based missile defense system in Alaska has successfully intercepted separating targets in five out of eight attempts."This test is very important and I'll go as far as to say historical," said Rear Adm. Kathleen K. Paige, program director of the sea-based missile defense project. "It verifies ballistic missile defense is real, that it is available today operationally at sea."Senior representatives from the navies of Australia, Germany, Japan, the Netherlands and Spain watched the test with Paige on the Hawaiian island of Kauai.The Missile Defense Agency plans to conduct three more sea-based tests next year.The Lake Erie is equipped with technology that allows it to detect and track intercontinental ballistic missiles. Since last year, U.S. warships the ICBM tracking technology have been patrolling the Sea of Japan, on the lookout for missiles from North Korea.North Korea shocked Tokyo and other nations when it test-fired a ballistic missile over northern Japan in 1998. Analysts say North Korea is developing long-range missiles capable of reaching Alaska, Hawaii or perhaps America's West Coast.Copyright 2005 The Associated Press. All rights reserved.This material may not be published, broadcast, rewritten, or redistributed.