When Charles Heller retired from the Army in 1996, he never thought he would be recalled to active duty seven years later at the age of 60.

But on New Year’s Eve, Heller, of Lawrence, got his marching orders. A week ago, he traveled to Washington, D.C. And now he is working in the Pentagon preparing a chronology of the Iraq war for the Joint Chiefs of Staff.

Heller had mixed emotions about returning to military life.

“It’s bittersweet,” he said last week in a telephone interview from his apartment in Falls Church, Va., near Washington. “It’s also kind of flattering.”

Heller had expected to continue spending his retirement with his wife of three years, playing with his grandchildren and teaching military and strategic studies at Washburn University in Topeka.

Even though Heller, who retired as a colonel, was still eligible to be activated for duty until the age of 68, he received a polite call from an Army officer asking whether he would return.

“It’s kind of hard to say no,” Heller said.

He will be poring over thousands of military documents from which to cull information for his chronology. He described it as a “monumental task” but one he thinks he is suited for because of his 30-year military career, knowledge of military history and experience as a writer and a teacher.

“History for history’s sake is OK but the military uses it for a purpose,” Heller said. “I’m going to look for things that are relevant to the future and the present in terms of the new 21st century warfare.”

The war with Iraq is the first war of the new century, he said. The first war with Saddam Hussein 13 years ago marked the end of the Cold War-era style of war.

Against Iraq in 1991, the U.S. military used tactics and equipment designed for a full-scale ground and air war against the Soviet Union, Heller said. Today the United States is the only remaining superpower and has military technology that is far beyond what was available in the first Gulf War, he said.

“The armed forces are just a magnificent machine,” Heller said. “It’s truly amazing what we are capable of doing.”

Unlike the Cold War era, however, Heller said the military would have to be more balanced among its forces. There would be more use of special operations units such as Army Rangers, and the methods for handling air and naval transport would require new thinking, Heller said.

Heller’s family heritage involves military service. His father was a combat photographer during World War II. When he was in the fifth grade, Heller’s mother gave him his great-grandfather’s Civil War discharge papers.

“He had been a drummer boy,” Heller said of his great-grandfather. “That was when I got interested in military history.”

Heller has a master’s degree and doctorate from the University of Massachusetts, where he focused on the post-Civil War Reconstruction period. He has taught at both the Command and General Staff College at Fort Leavenworth and the Army War College in Carlisle, Penn.

Heller also has written and edited several books, including “America’s First Battles” and a biography of George Luther Stearns, who was the leader of the Secret Six group that financed abolitionist John Brown.

Heller’s wife, Michelle Heller, will continue to live in Lawrence. She also had mixed emotions about her husband leaving for what could be a two-year tour of duty.

“I’ll miss him,” she said. “But this is an opportunity — sort of the capstone of his career. He loves the military and he loves to write.”