TOKYO >> U.S. Defense Secretary Ash Carter said Monday he believes his designated successor, if confirmed by the Senate as expected, will be a quick study regarding the responsibilities of the office.

Carter declined to offer his view of whether President-elect Donald Trump’s choice of retired Marine Gen. James Mattis undermines the principle of civilian control of the military.

Because Mattis has been out of uniform for fewer than seven years, which is the minimum required by law, his nomination will require new legislation to override the prohibition. Mattis, 66, retired in 2013 as a four-star general. He is a combat veteran of the wars in Iraq and Afghanistan and is a former head of U.S. Central Command.

In an interview with reporters flying with him to Tokyo, Carter declined to comment directly on questions about preserving the principle of civilian control of the military. Mattis would be the first retired military general to serve as defense secretary since George Marshall in 1950-51.

“I think that will be taken into account by the Congress,” Carter said, adding that “they (the Congress) have made provision that this is possible, in the law, expecting that on occasion this may be a president’s choice, and also an appropriate choice, as seen by Congress.”

In fact it will take a separate act of Congress to make an exception allowing Mattis to serve as defense secretary.

Carter offered strong praise for Mattis.

“He’s an extremely capable person,” Carter said. “I’ve known him literally for decades.”

“Not only am I committed to helping him to hit the ground running, but it will be an easy thing to do because I know him well enough, I’ll help him every way I can.”