William Withuhn, a licensed locomotive engineer who, during his 27 years as transportation curator at the Smithsonian National Museum of American History, could have been called America’s official train collector, died June 29 at his home in Burson, California. He was 75.

The cause was heart disease, said his wife, Gail Withuhn.

Withuhn was an expert on all modes of transportation — planes, trains and automobiles — and helped the American History Museum acquire many major items, including Richard Petty’s No. 43 Pontiac stock car, which he drove for his 200th and final NASCAR victory.

Withuhn also was a sports-car enthusiast who had flown more than 200 combat missions as a navigator in the Vietnam War, but his greatest fascination was with trains. He grew up in the railroad town of Modesto, California, and while still in his 20s received his engineer’s certification.

He later operated short-line railroads in Virginia, Maryland, Delaware and New York and became a railroad historian, preservationist and advocate in Congress before turning his love of transportation into a career at the Smithsonian.

In 1981, Withuhn helped prepare the Smithsonian’s 1831 John Bull locomotive, the oldest self-propelled vehicle in North America, for a short run in Georgetown.

“Americans ride the trains in their hearts,” he wrote in a 2002 essay for Newsday. “Trains built America, physically interlacing a huge geography and splintered political regions into a national union. … We became the most mobile nation in the late 19th century, with trains.”

After becoming the history museum’s transportation curator in 1983, Withuhn sought to show how the country’s development, and even its spirit of restless adventure, was intertwined with various modes of transport.

He oversaw more than 20 major exhibitions and was instrumental in developing a 26,000-square-foot permanent transportation exhibit, “America on the Move,” which opened in 2003. It was the largest single exhibit undertaken by any Smithsonian museum, up to that time.

In addition to locomotives, complete with the sounds of their whistles, the exhibit included a patch of pavement from Route 66, the westward-leading highway, streetcars, a school bus, a 1940s hot rod, motorcycles and cars of various vintages.

Withuhn helped coordinate the installation of all these vehicles, often requiring elaborate hydraulic lifts, winches and vast amounts of patience.

“I call them iron sculptures in an industrial garden,” he said in 2000.

In addition to his curatorial duties, he also raised more than $30 million for “America on the Move” and other Smithsonian endeavors.

William Lawrence Withuhn was born Aug. 12, 1941, in Portland, Oregon, and grew up mostly in Modesto. His father was an accountant.

At the University of California at Berkeley, he was cadet commander of the ROTC unit. After graduating in 1963, he joined the U.S. Air Force but learned that, at 6-foot-4, he was too tall to become a pilot.

There were no height restrictions for navigators, however, and Withuhn expected to become a navigator on transport planes. During the Vietnam War, he was assigned to a gunship and participated in more than 200 missions, most of them at night. He received two Distinguished Flying Crosses and the Bronze Star. He left the Air Force in 1972 as a captain and later served in the Air Force Reserve.

In the mid-1970s, he was on the staff of U.S. Rep. James Hastings, R-New York, and worked on the Regional Rail Reorganization Act. Withuhn also attended graduate school at Cornell University in the 1970s, receiving two master’s degrees, one in business administration and another in history.

He was acting director of the Railroad Museum of Pennsylvania in the early 1980s before joining the Smithsonian.

Withuhn was the editor of “Rails Across America,” a 1993 history of railroads, and the author of another book on trains, “Spirit of Steam” (1995). He completed a manuscript on the history of 20th-century steam locomotives before his death.

After retiring in 2010, Withuhn worked with the National Museum of African American History and Culture to restore and install a Jim Crow-era segregated railroad car from the 1940s.

Survivors include his wife of 52 years, Gail Hartman Withuhn of Burson; two sons, Thomas Withuhn of Eldersburg, Maryland, and Harold Withuhn of San Francisco; a brother; and a grandson. Another son, James Withuhn, died in 1994.

On weekends, Withuhn traveled across the country to speak at gatherings of railroaders and to take part in train demonstrations, often in the engineer’s cab.

“What makes industrial history important today,” he told the Modesto Bee in 2000, “is that we need to be reminded that the people who built this country physically were blue-collar workers. … These were people who never finished grade school, some of them, and they had many of the same skills and responsibilities as the captain of a 747 jet. … There was civilization before the computer: we need to appreciate that.”