Before he became known as the father of artificial Christmas trees, Si Spiegel was a brave Army aviator. In the final days of World War II, he piloted his B-17 Flying Fortress in an armada of 1,500 Allied bombers that pounded Berlin. Hit by anti-aircraft fire, two of the plane’s four engines lost power as Spiegel changed course to return to England.

Rather than bail out Germany and risk capture as a prisoner of war (especially considering he was Jewish), Spiegel managed a crash landing in Soviet-occupied Poland. After being trapped there for weeks, he improvised a daring escape, using parts of his own aircraft to manipulate another B-17 that had crashed near him, and then flew to an American base in Italy.

Spiegel, who died at age 99 on Jan. 21 at his Manhattan home, was one of the last surviving American B-17 pilots of World War II, said his granddaughter Maya Ono. But Spiegel, a machinist by training, has another legacy: He was considered a pioneer of the mass-produced artificial Christmas tree.

The son of Jewish immigrants from Eastern Europe, he grew up in a religious neighborhood of Brooklyn and never had a Christmas tree, natural or artificial, during his childhood.

“I don’t necessarily think my grandfather was associated with trees and Christmas as much as he was with the machinery he built to make the trees,” Ms. Ono said, “and then, later in life, the systems he created to build a successful business and the relationships it cultivated.”

For Spiegel, becoming the king of artificial Christmas trees was a coincidence, but his religion did play a role. After the war, he applied to be a commercial pilot, but was told he was barking up the wrong tree.

“They were blatant about it,” he said in an interview with the New York State Military Museum in 2010. “It’s not that they gave you any excuse. They told you: ‘We don’t hire Jews.’”

He briefly enrolled at the City College of New York to become an engineer, but after his time in the war he found the academic routine disturbing and stultifying. After a brief stint as a radio host in New Mexico, he returned to New York.

Taking advantage of his initial training in the military, he was hired as a machinist, but was unable to hold down a regular job due to his role as an organizer for the United Electrical Workers Union, which had been branded by its parent, the Congress of Industrial Organizations, as being plagued by of communists. (Mr. Spiegel was later president of the Machinists Union Local 1709, which belonged to the AFL-CIO.)

In 1954, he finally landed a permanent position at American Brush Machinery Company, based in Mount Vernon, New York. He operated machines that made wire brushes and other materials for various industrial functions, including cleaning and scrubbing wood and metal finishes.

Artificial Christmas trees had been made for decades, originally with the same animal hair bristles used for toilet brushes, then with aluminum, and finally with different forms of plastic.

After American Brush unsuccessfully expanded into the Christmas tree business, Mr. Spiegel, by then a senior machinist, was tasked with closing the artificial tree factory. Instead, he began studying natural conifers, modified brush-making machines to emulate real trees, and patented new production techniques.

He left the renamed American Tree and Crown Company in 1979 and founded Hudson Valley Tree Company two years later, which began mass-producing 800,000 trees a year on an assembly line that produced one every four minutes.

By the late 1980s, his company was generating $54 million in annual sales and employed 800 workers in Newburgh, New York, and Evansville, Indiana. He sold Hudson Valley Tree Company in 1993, retired as a multimillionaire and turned his attention to cultural and educational pursuits. and philanthropy for social justice.

Yes Spiegel was born on May 28, 1924 in Manhattan. His mother, Massia (Perlman) Spiegel, a seamstress and suffragette born in Bessarabia, named him after Issai or Isaiah, the biblical prophet who expressed the utopian dream that “they will not learn war anymore.” His father, David, born in Ukraine, owned a laundromat in Greenwich Village.

After graduating from Straubenmuller Textile High School in Manhattan in May 1942, he worked operating grinding machinery for an industrial equipment manufacturer for four months and then enlisted in the Army.

He graduated from the aviation mechanics school at Roosevelt Field on Long Island, but he was frustrated: he wanted to fly airplanes, not repair them.

“How could I fight Hitler with a wrench?” he told The New York Times in 2021.

He was referred to Mitchel Field, two miles away, where he became an aviation cadet. During his training, he married Frankie Marie Smith in New Mexico; After the war, they divorced.

He was sent to Eye, England, near the North Sea, where his motley crew consisted of another Jew, five Catholics, a Mormon, and a criminal who had been given the option of going to prison or enlisting in the army.

Returning from his 33rd mission, the massive February 3, 1945, air raid on Berlin, Spiegel managed to land face down in a frozen potato field in Reczyn, Poland. Although the crews’ families were informed that their relatives were missing in action, Russian troops held them.

Not knowing what to do with their supposed allies, the Russians waited for orders from their superiors. But rather than sit still, Spiegel and his fellow officers surreptitiously removed an engine and tire from their own plane to repair another disabled B-17 that had crashed nearby. They bartered for fuel and, on March 17, the combined crews escaped to Foggia, Italy, where they were able to notify their families back home that they had survived. Mr. Spiegel led two more missions and then returned to New York on August 31, 1945, but would return to England and Poland to rejoin his crew from the 849th Bombardment Squadron of the 490th Bombardment Group.

Mr. Spiegel joined Pete Seeger’s Good Neighbor Choir and in 1949 attended Camp Unity, a Communist-affiliated summer camp in Wingdale, New York, where he met Motoko Ikeda, the daughter of Japanese immigrants who had established in California. During the war, she and her family had been imprisoned in an internment camp in Wyoming; Afterwards, her parents returned to California and she went to New York. She and Spiegel married in 1950. Spiegel, who became an artist, died in 2000.

Since then, Mr. Spiegel had lived alone on the Upper West Side, not far from where he was born.

He is survived by his daughter, Sura Kazuko Ono; two sons, Ray Spiegel and Tamio Spiegel; his brother Lee; and five granddaughters.

Spiegel celebrated the Jewish holidays with his children, but when they were little, a Christmas tree was a winter holiday staple: first a real one, then the best of the fake ones.

“They were pagan symbols,” he told The Times. “My kids liked them.”

His wife also maintained a cultural imprint that was not part of her upbringing: “Motoko was better at Jewish food than my mother,” he said. “She could cook in any language.”