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John Limbert stepped down Friday as head of the State Department's Iran desk. In 1979, Limbert was one of 52 Americans taken hostage during the Islamic Revolution. He was held for more than a year. Brad Horn/NPR hide caption

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Brad Horn/NPR

Staff members at the Army Experience Center in Philadelphia demonstrate the Humvee interactive simulator in 2009. Matt Rourke/AP hide caption

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Matt Rourke/AP