As defense secretary to a president who famously envisioned "a world without nuclear weapons," Ash Carter has said remarkably little about them.

He has been quiet on a range of nuclear issues, including the Pentagon's $8 billion effort to correct an array of morale, training, discipline and resource problems in the Air Force nuclear missile corps, revealed by The Associated Press in the last three years. Nor has he publicly explained in detail the utility of nuclear weapons, in an age of attacks by non-state actors like the Islamic State, to build support for spending hundreds of billions on a new generation of them.

When asked, he has left no doubt that he sees nuclear weapons as the "bedrock" of U.S. security. But he rarely reveals the underpinnings of his thinking.

This is all the more notable because Carter, a physicist by training and policy wonk by reputation, cut his professional teeth on nuclear weapons during the Cold War. He probably knows more about them than any defense secretary since William Perry, a longtime nuclear expert, led the Pentagon a generation ago.

This quiet approach is expected to end when Carter visits Minot Air Force Base in North Dakota on Monday. There, he plans to deliver a speech on nuclear deterrence, the notion that a robust and ready U.S. nuclear force will make clear that the cost of hitting the U.S. would outweigh any benefit. It will mark his first visit to a nuclear weapons base since becoming defense chief in February 2015.

Minot is home to Minuteman 3 intercontinental ballistic missiles that stand in underground silos, ready for nuclear war. A portion of the Air Force's B-52 bomber force, including a number equipped to carry nuclear bombs, also are at Minot.

Like the three other men who have run the Pentagon for President Barack Obama, Carter has plenty of other high-priority issues to consume his time and attention, including the war against the Islamic State group. Carter also has chosen to focus on what he calls the "force of the future" — a set of policy initiatives meant to modernize the way the defense establishment recruits and develops members of the armed services. And he has given a great deal of attention to Silicon Valley and other technology hotbeds that he sees as potential keys to translating civilian innovation into U.S. military advantage.

Nuclear weapons issues have taken a back seat, at least publicly.

"Secretary Carter has not said much on nuclear weapons, but his actions speak volumes," says Joe Cirincione, president of the Ploughshares Fund, an advocacy group that argues for nuclear reductions and against the administration's plan to commit hundreds of billions to build a next-generation nuclear arsenal. "He has been the Dr. No of nuclear reductions, defending every program contract and resisting every cut in the nuclear force."

A spokesman for Carter disputes that the Pentagon chief has been quiet about nuclear issues.

"He regularly speaks about the importance of the nuclear triad to our security, its importance in reassuring our allies and deterring potential adversaries, and the need to ensure that we maintain and modernize that capability," said Gordon Trowbridge, the Pentagon's deputy press secretary.

Carter has talked quite a lot about the nuclear weapons of other countries. He chastised Russia for nuclear "sabre rattling," endorsed the U.S. nuclear deal with Iran and criticized what he has called North Korea's nuclear "pursuit and provocations." But when it comes to America's own weapons, he has mostly limited himself to broad references to their importance.

Before this week, Carter had not given a speech about nuclear weapons nor visited a nuclear weapons base. His immediate predecessor, Chuck Hagel, visited two of the three Air Force bases that operate Minuteman 3 missiles, plus one of the two Navy bases for Trident nuclear submarines. Hagel also visited a B-2 bomber base to highlight his support for an Air Force's plan to build a new nuclear bomber.

Among Carter's most substantial remarks about nuclear weapons was his response earlier this month to a question from a student at the University of Oxford in England after Carter spoke about the American defense relationship with Britain. Carter was asked whether he worries that important nuclear issues are being ignored or neglected.

"Well, it's a blessing to be able to take the public's mind off the nuclear question," Carter began. He said he was thankful that nuclear issues are "not in the headlines."

He called deterrence the cornerstone of U.S. strategic defense policy because "we've never found another way to manage the unprecedented risk inherently posed by the technology of nuclear weapons." He added, "we're going to have nuclear weapons as far into the future as I can see. And they need to be safe, they need to be secure, they need to be reliable."

"Fortunately you don't see us using" nuclear weapons, Carter said in response to a question last week from a sailor at the Pentagon. "And that's a good thing." Nuclear weapons, he said, are "there in the background as a guarantor of our security."

During his long career as a national security specialist, Carter has written extensively about nuclear weapons issues. In a 1985 article titled "The Command and Control of Nuclear War" he dissected the intricate issue of how wartime decisions would be communicated to and executed by the nuclear force. He was the lead author of a report, "Crisis Stability and Nuclear War," in 1987, again examining nuclear command and control issues.

During Bill Clinton's first term in the White House, Carter served as assistant secretary of defense for nuclear security and counter-proliferation.