Fort Riley ? For 16 months, Lt. Col. John Nagl has trained teams of advisers at Fort Riley for a year’s duty in Afghanistan or Iraq, part of the Army’s effort to build up those nations’ security and fight terrorism, using teams grounded in the principles of fighting insurgents.

But now he’s moving on. Nagl is retiring from the Army after 24 years and joining the Center for a New American Security – a Washington think tank that includes among its directors former Secretary of State Madeleine Albright, Defense Secretary William Perry and John Podesta, chief of staff for President Clinton.

A West Point graduate and Rhodes Scholar, Nagl’s retiring to spend time with his wife of 15 years, Susanne, and their 6-year-old son, Jack.

“There are lots of sacrifices inherent in military life. The most serious of those aren’t made by the soldier, they’re made by the family,” Nagl said earlier this week. “Ultimately, I decided that it was the best thing to do for my family, given that I could still do the things I find most interesting, but I could also give my family some things that they want – and I believe deserve – after 15 years of following me around.”

The center published Nagl’s proposal last summer to create a standing adviser corps. Such a force, trained and used properly, could lessen future needs for committing large numbers of American forces.

Jim Miller, the center’s senior vice president and director of studies at CNAS, describes Nagl as articulate and a leader. He said Nagl’s departure is a loss for the Army but said the lieutenant colonel will remain “a change agent,” even outside the military.

“John has a unique ability to understand current situations and to anticipate future trends and then develop innovative approaches to coping with them,” Miller said.

Nagl, 41, gained acclaim for his book, “Learning to Eat Soup with a Knife,” a phrase taken from T.E. Lawrence of Arabia’s “Seven Pillars of Wisdom.” Lawrence led an insurgency against the Turks during and after World War I.

He’s done his work to date in his spare time when he’s not serving as a battalion commander at Fort Riley. He’s given hundreds of lectures and interviews, including an appearance on “The Daily Show.”

Nagl often teaches two classes of advisers a day, mixing a blunt assessment of the counterinsurgency fight with humor and self deprecation.

“I’m just a lieutenant colonel in a mobile home in Fort Riley, Kansas,” Nagl said, referencing the temporary structures housing the transition team mission.

But his counterinsurgency expertise is rooted in fighting two wars in Iraq and earning a doctorate from Oxford in international relations. His credentials caught the eye of Gen. David Petraeus when he was commander at Fort Leavenworth. Petraeus plucked Nagl to be a writer of the Army-Marine counterinsurgency manual, the first significant publication on the topic in more than 20 years.

Completed in 2006 and downloaded more than 1.5 million times in the first month, Petraeus used it as the basis for his war strategy after taking command of forces in Iraq in 2007.

“We know the enemy is reading it. Now, we just have to get our guys reading it,” Nagl said.

Nagl isn’t alone in thinking the adviser mission merits attention. In 2006, then-Defense Secretary Donald Rumsfeld established the Joint Center for International Security Force Assistance at Fort Leavenworth. Under the direction of Lt. Gen. William Caldwell, the center is supposed to make sure the best practices learned in adviser missions are put to use throughout the military and by other coalition forces.