Excerpted from Locomotive by Brian Floca. Copyright 2013 by Brian Floca. Excerpted by permission of Simon & Schuster Children's Publishing. Courtesy of Simon & Schuster Children's Publishing hide caption

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Robert Gates in June 2011 during his final official news conference as secretary of defense. Jason Reed /Reuters/Landov hide caption

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Robert Gates on the emotions he felt when writing condolence letters

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