Gilbert Seltzer, who served with a secret Army unit in World War II that fooled German forces with inflatable tanks, dummy airplanes, fake radio transmissions and sound effects that mimicked troop movements, died on Aug. 14 at his home in West Orange, N.J. He was 106.

His son, Richard, confirmed the death.

Mr. Seltzer was one of 1,100 soldiers attached to the 23rd Headquarters Special Troops, which pulled off elegant strategic cons on German forces, ingeniously creating the illusion that American troops were where they weren’t.

Shortly after the war, the 23rd became known as the Ghost Army. In later years Mr. Seltzer, who at his death was the oldest surviving Ghost Army soldier, became a public ambassador for the veterans of the unit.

“We would move into the woods in the middle of the night, going through France, Belgium and Germany, and turn on the sound” — from blaring loudspeakers — “so it sounded like tanks were moving on the roads,” Mr. Seltzer told StoryCorps in 2019. “The natives would say to each other, ‘Did you see the tanks moving through town last night?’”

“They thought they were seeing them,” he added. “Imagination is unbelievable.”

Mr. Seltzer, an architect, was a platoon leader and later a lieutenant and adjutant of the 603rd Engineer Camouflage Battalion, whose ranks included men who would go on to work in advertising, art, architecture and illustration, among them the future fashion designer Bill Blass, the photographer Art Kane and the painter Ellsworth Kelly.

The battalion handled the Ghost Army’s visual fakery; the 3132nd Signal Service Company was in charge of sound deception; the Signal Company, Special, devised realistic-sounding radio messages to throw off the Germans. The 406th Combat Engineer Company provided security.

In March 1945, in one of their most elaborate feats of trickery — during the critical Rhine River campaign, designed to finally crush Germany — the 23rd set up 10 miles south of the spot where two American Ninth Army divisions were to cross the river. To simulate a buildup of those divisions at their decoy location, the Ghost Army used inflated tanks, cannons, planes and trucks; sent out misleading radio messages about the American troops’ movements; and used loudspeakers to simulate the sound of soldiers building pontoon boats.

The Germans fell for the ruse, firing on the 23rd’s divisions, while Ninth Army troops crossed the Rhine with nominal resistance.

Mr. Seltzer, who had flown in a reconnaissance mission before the crossing to determine if the 23rd’s preparations were adequate, told StoryCorps: “We are credited with saving as many as 30,000 men, which I think is an exaggeration. But if we saved one life, it was all worthwhile.”

The work of the 23rd was recalled in a 2013 PBS documentary, “The Ghost Army,” produced by Rick Beyer. Two years later Mr. Beyer collaborated with Elizabeth Sayles on the book “The Ghost Army of World War II: How One Top-Secret Unit Deceived the Enemy With Inflatable Tanks, Sound Effects, and Other Audacious Fakery.”

The Ghost Army was also the subject of an exhibition at the National World War II Museum in New Orleans that opened in early March 2020. The museum was closed soon after until Memorial Day because of the coronavirus pandemic; after the museum reopened, the exhibition was on view until January.

Mr. Beyer has campaigned to have the Ghost Army receive the Congressional Gold Medal; legislation passed the House this year and is pending in the Senate.

“Gil was extremely proud of what he did in the Ghost Army, but at the same time found it fairly amusing that people were interested in something he spent one year on 75 years ago,” Mr. Beyer said in a phone interview. “Like most of the guys in the unit, he was struck by how their role was saving lives. They weren’t about killing people but using creativity that could save American lives and even some German lives.”

With Mr. Seltzer’s death, Mr. Beyer said, there are now only nine Ghost Army soldiers left.

Mr. Seltzer was born on Oct. 11, 1914, in Toronto to Julius and Marion (Liss) Seltzer, Russian immigrants. His father owned a knitting mill and was an anarchist whose friends included his fellow anarchist Emma Goldman. His mother was a homemaker.

Gilbert studied architecture at the University of Toronto, where he received a bachelor’s degree, then worked for an architectural firm in Manhattan. He enlisted in the Army in 1941, trained at Pine Camp (later Fort Drum) near Watertown, N.Y., and attended officer candidate school in Belvoir, Va., before being assigned to the 603rd.

In Mr. Beyer’s documentary, Mr. Seltzer recalled his early reaction to being told that the purpose of the 23rd’s preparations was to have the enemy fire at him and his fellow soldiers.

“We came to the conclusion,” he said, “that this was a suicide outfit.”

Mr. Beyer said that three members of the Ghost Army were killed and about 30 wounded. He suggested two reasons for the relatively small number of casualties: The unit projected great force through its deceptions, possibly repelling the enemy; and the soldiers were not always at the front, which minimized their vulnerability.

After the war, Mr. Beyer returned to architecture. Over the years he designed the Utica Memorial Auditorium in Utica, N.Y. (now the Adirondack Bank Center), which is renowned for its cable-suspended roof system; buildings at West Point and the U.S. Merchant Marine Academy; and the East Coast Memorial in Battery Park, in Lower Manhattan, which honors soldiers, sailors, Marines, Coast Guardsmen, merchant mariners and airmen who died in battle in the Atlantic during World War II. He continued to work until January 2020.

In addition to his son, Mr. Seltzer is survived by two grandchildren and three great-grandchildren. His wife, Molly (Gold) Seltzer, died in 1994.

One night in July 1944, soldiers of the 603rd were on a farm in Normandy, where they moved an antiaircraft battery and replaced it with a rubber one, part of an operation to cover the movement of the Second Armored Division with dummy tanks and guns to fool the Germans into thinking the division had not left.

The farmer, who was angry about the noise that had been made by the real guns, approached the soldiers and said, “Encore boom boom?,” banging his fist on a gun, not knowing it was a fake.

“His hand bounced up and down and he said, ‘Boom boom ha ha,’” Mr. Seltzer told Mr. Beyer in the interview filmed for the documentary but not used. “That became a byword in the 603rd.”