Harry W. Pfanz, a Civil War historian who wrote an acclaimed trilogy of the Battle of Gettysburg, a bloody clash in July 1863 that turned the tide of the war in the North’s favor, died Jan. 27 at his home in Gaithersburg, Md. He was 93.

The cause was renal failure, said a son, Donald Pfanz.

Dr. Pfanz was a former chief historian of the National Park Service and, earlier, the historian of Gettysburg National Military Park in Pennsylvania.

Three of his great-grandfathers were Union veterans of the Civil War, and one of them was still living when Dr. Pfanz was in high school. As a result, he said, “I grew up with an interest in the Civil War as far back as I can recall.”

After retiring from the Park Service in 1981, Dr. Pfanz spent the next 20 years researching and writing his Gettysburg trilogy: "Gettysburg: The Second Day" (1987), which was the most critically praised book in the trilogy; "Gettysburg: Culp's Hill and Cemetery Hill" (1993); and "Gettysburg: The First Day" (2001).

In an Atlantic Monthly review of “The Second Day,” New York Times columnist Tom Wicker wrote, “Pfanz appears to have found out everything that can be known about the fighting on July 2, about the maneuverings that led to it, about the armies that collided so fatefully in the rolling Pennsylvania farm country, and about the men who led them — right down to the sergeants and lieutenants, without whom armies seldom would be led anywhere.”

Harry Willcox Pfanz was born Dec. 9, 1921, in Bexley, Ohio, and grew up on a farm.   In 1943, he graduated from Ohio State University. Then, he served in the Army in Europe during World War II. He was wounded in action during the Battle of the Bulge.

He became an Army Department historian and, from 1956 to 1966, was the historian at Gettysburg. He received a doctorate in history from Ohio State University in 1958.

In 1966, he took a job at the Gateway Arch in St. Louis and was superintendent when it opened to the public in 1968. He left St. Louis in 1971 to return to Washington, where in 1974 he became chief historian of the National Park Service, a position he held until retirement.

Dr. Pfanz’s wife of 56 years, Letitia Earll Pfanz, died in 2008. A daughter, Letitia Elizabeth Pfanz, died in 1964.

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Survivors include three children, Frederick Pfanz of Westerville, Ohio, Donald Pfanz of Fredericksburg, Va., and Marion Ake of Woodsboro, Md.; and five grandchildren.