Harry W. Pfanz, a Civil War historian and author who wrote an acclaimed trilogy of the Battle of Gettysburg in July 1863, a bloody clash 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 the 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).