A Government Accountability Office document indicates the Pentagon reported the type of ground-based interceptors that would be deployed in Europe didn't hit targets in five of 13 tests, USA Today reported.
In the most recent test of the U.S.-based system, an interceptor launched in from California destroyed a warhead launched from Alaska, officials said. The test was to determine whether the interceptor could differentiate a live warhead from decoys but the decoys didn't deploy.
U.S. President Barack Obama recently indicated he could consider abandoning the Europe system in exchange for Russia's help in blunting Iran's nuclear aspiration. Russia has opposed the shield development, saying it threatens the country's national security
The Congressional Budget Office indicated the system, planned as a potential shield against attacks, would cost $9 billion to $13 billion, and would leave parts of Europe exposed to an Iranian missile attack.
Independent technical analysis indicates Iran and North Korea, which has a nuclear program, could trick the system by using something as simple as balloons, David Wright of the Union of Concerned Scientists told USA Today.
"Do I believe with any confidence that this system would be able to stop a nuclear attack? The answer is no," Wright said.
Richard Lehner, spokesman for the U.S. Missile Defense Agency, said in an e-mail message to USA Today the tests are "as operationally realistic as possible."
The GAO told Congress in February the type of system proposed for Europe, is partly in place in the United States and "continues to experience testing problems and delays."
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