On a corner shelf in his expansive offices near Judiciary Square, Judge James Baker has a collection of hats. They are mostly hats worn during war time, and they come from around the world.

Baker has worn the hat of a warrior, graduating first in his class at Officer Candidates School to earn a commission as a second lieutenant in the Marine Corps. But it is quickly evident that he wears many other hats as well, most recently as a judge on the United States Court of Appeals for the Armed Forces and an adjunct professor at the Georgetown University Law Center and University of Iowa College of Law. After a few moments, it is easy to see him wearing the hat of fatherhood, as references to his children are frequent and lengthy, and nearly every nook and cranny of his office is adorned with a child’s drawing or toy. He once wore the hat of an aide to former Sen. Daniel Patrick Moynihan (D-N.Y.), a man whom he holds in high regard, and of legal adviser to the National Security Council, where he advised former President Bill Clinton, among others, on U.S. and international law as it pertained to national security.

What better qualifications, then, to wear the hat of author of the book “In the Common Defense: National Security Law for Perilous Times.” Published this summer by Cambridge University Press, the book is a guide for national security law and process from an insider’s perspective, and written, the author hopes, in a manner accessible to policy readers as well as lawyers. Among other things, it makes the point that “good faith application of law results in better security at the same time that it honors America’s commitment to the rule of law.”

“In the Common Defense” comes at a time when security is at the top of the national agenda; it is most definitely at the top of Baker’s agenda. His goal is to continuously engage himself in public service, if possible, through the judicial process, government service and teaching.

“It would be my hope to continue to contribute to law,” he said.

His book does just that, by broaching a topic with which he is intimately acquainted. Law, as he puts it, is “not an abstraction, but intended to address real world threats while allowing us to uphold our constitutional values by doing so.” The reason it may not do this, he said, is because of disagreement about the threat or responses to it.

As a result, Baker starts his book with a description of what he perceives as the principal threats ahead, including the threat of nuclear terrorism. He also is concerned that leaders may consider security and liberty as presenting a zero-sum equation, and compromise in a manner that diminishes our security and constitutional fabric rather than seeking preferred outcomes that seeks to maximize both values. In his view, the executive must have broad and flexible authority to act, but be subject to a process of meaningful internal and external appraisal.

Though his book deals with a number of controversial subjects, Baker was disinclined to comment on them.

“Part of being a judge is to be impartial in issues that come before them,” he said. “In writing this book, I took the same tack. I did my best to articulate law, making it clear where there was agreement, and clear where there was not.”

At 325 pages, not including notes and attachments, the book may not bring understanding of national security law to non-lawyers or those not already interested in the intricacies of national security law. But it’s a fair trade-off when considering the importance of delving into issues as complex as the ones he tackles.

Evidence of Baker’s ability to impartially discuss complex topics was given at his investiture ceremony as 18th judge of the U.S. Court of Appeals for the Armed Forces by former Attorney General Janet Reno.

“He would come into my office with his locked bag in hand, in his measured way, and he would make the most forceful, accurate, considered argument for one position,” Reno said. “He would then pause and go on and set forth the most forceful, accurate and considered argument for the other side. He would then pause, and then he would tell me what he thought of the competing arguments, where the flaws were and where the strengths were.”

When he is not wearing the hat of a judge and author, he is wearing a hockey helmet, serving as goalie for his local team called “The Predators.” But his main hobby, he said, is a good game of hide-and-seek, which he plays with his children Grant, 4, and Jamie, 7.

“Any day I get to play hide-and-seek with the kids is a good day,” he said.

The statement complements the children’s watercolor pictures taped to nearly every wall in his office. His children, it seems, are the only reason he takes off every hat he has to hand them to his wife, Lori, of 15 years.

“Her job is just as hard as mine, if not harder,” he said.