Navy SEALs participate in special operations urban combat training in 2012. The training exercise familiarizes special operators with urban environments and tactical maneuvering during night and day operations. Mass Communication Spc. 2nd Class Meranda Keller/U.S. Navy hide caption

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Mass Communication Spc. 2nd Class Meranda Keller/U.S. Navy

President Trump, with Defense Secretary James Mattis, shows his signature on an executive action to rebuild the military, during an event at the Pentagon on Friday. Susan Walsh/AP hide caption

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Susan Walsh/AP

The Pentagon says many of the ISIS fighters targeted in Wednesday's strike escaped from the former ISIS stronghold of Sirte, shown here during fighting in September. Manu Brabo/AP hide caption

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Manu Brabo/AP

A Marine Fighter Attack Squadron 121 F-35B Lightning II prepares to make a vertical landing in Yuma, Ariz., in 2013. President-elect Donald Trump asked Boeing to price a version of one of its fighter jets to be competitive with Lockheed Martin's F-35 aircraft. Cpl. Ken Kalemkarian/U.S. Marines hide caption

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Cpl. Ken Kalemkarian/U.S. Marines

A Navy file photo shows T-AGS 60 Class Oceanographic Survey Ship, USNS Bowditch. The Navy says the ship's mission includes oceanographic sampling and data collection and the handling, monitoring and servicing of remotely operated vehicles (ROVs), among other things. U.S. Navy hide caption

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U.S. Navy

President Obama speaks to the media after a meeting with Secretary of Defense Ashton Carter and members of the Joint Chiefs of Staff at the Pentagon on Thursday in Arlington, Va. Mark Wilson/Getty Images hide caption

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Mark Wilson/Getty Images

Secretary of Defense Ash Carter (left) says the Pentagon's new hacker program will strengthen America's digital defenses. Carter is seen here with the chairman of the Joint Chiefs of Staff, Gen. Joseph Dunford. Mark Wilson/Getty Images hide caption

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Mark Wilson/Getty Images

A lawsuit challenging the constitutionality of an all-male military draft could be revived, after the Pentagon changed its policy on women in combat. Here, soldiers attend a ceremony in Arlington, Va., earlier this year. Chip Somodevilla/Getty Images hide caption

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Chip Somodevilla/Getty Images

Defense Secretary Ash Carter is expected to announce that women can now serve in front-line combat posts. Here, Carolina Ortiz moves away from a 155-mm artillery piece after loading it during a live-fire exercise at the Marine base in Twentynine Palms, Calif., earlier this year, during a months-long study of how women might perform in ground combat jobs. David Gilkey/NPR hide caption

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David Gilkey/NPR