These organizations have survived thousands of attacks over the years and they have invested in multiple layers of defense.

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The presence on flights of gun-carrying pilots traveling as passengers, federal air marshals and airline crew members trained in self-defense provide additional layers of security to protect against misuse of the items, he said.

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While it will still make sense to have multiple layers of defense against hostile missiles in which Aegis is only part of the solution, at present it is the part of the solution that looks most cost-effective.

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If the debt limit is reached and Congress does not act in time, however, all of these layers of defense will be breached and the nation will default on its obligations sometime between Feb. 15 and March 1.

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Kadish declared that such a layered system, comprised over time of a range of systems to address an evolving threat, would likely utilize sea- and space-based missile defense "layers" to complement and add robustness to the ground-based capability he is preparing for deployment in Alaska.

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