At the Museum of Science and Industry, the U-505's home for the past 50 years, he and fellow Navy veteran Wayne Pickels hid up top when groups came through.
The two ex-sailors would wait until they heard the tour guide tap his ring on the conning tower, then climb down the ladder into the control roomand tell their story.
"[The Germans] took the cover off the sea strainer to flood that thing, so naturally I had to stop the water," Mr. Lukosius told reporters in 2004. "But the thing is, we were told about booby traps."
The machinist groped blindly underwater for wires that might tell him an explosive device was there. He didn't find any, but did get his hands on the metal cover.
"If there's a booby trap . . . I'm going to sink us anyhow, but I've got to stop the water from coming in," he said. "So I put the cover on and the submarine didn't sink."
As Mr. Lukosius did so, Pickels recalled Monday, he said, "Here goes nothing."
Mr. Lukosius, 87, who won a Silver Star for his bravery, died Saturday at Ingalls Hospital in Harvey. An industrial roofer who worked with hot tar for 40 years, he died of a lung ailment likely caused by exposure to asbestos.
The South Holland resident will live on as part of the museum's new U-505 exhibit, introduced two years ago when the deteriorating sub was moved indoors and renovated. Mr. Lukosius figures prominently in a video, audio interviews and photos.
At 14, he helped support family

He was a modest hero, said his daughter Diana Siadak. "He said, 'I did what I was told -- we didn't think about the danger,' " she said. But he enjoyed telling the U-boat story. Many schoolchildren heard it, some as recently as May when he spoke at Calvary Academy in South Holland.
Golfing also helped occupy his retirement. Mr. Lukosius scored a hole-in-one on a course in Solon, Ohio, in the early 1980s.
Twenty years earlier he and buddy Al Dunlop played 54 holes in one day at Cog Hill in Lemont. Starting at sunup, "We walked because we didn't have enough money to rent a cart," Dunlop said.
It was drizzling and they had the course to themselves. One round turned into two, then three. "We came home as the sun was setting," Dunlop said.
He also was a talented bowler, with trophies to prove it.
Born in Chicago's Roseland community to Lithuanian immigrant parents, he helped support the family at age 14 after his father was killed by a streetcar. Mr. Lukosius told his children, "I made $8 a week, gave $7 to my mother and had a dollar for myself."
He enlisted after his brother Leo returned from war service. Two months before the U-505 incident, while he was on leave in New York City, his sweetheart, Dorothy Lebus, flew in and married him. She died in 1995.
Survivors in addition to Siadak include another daughter, Catherine Postma; a son, Paul, and seven grandchildren.
Visitation will be from 2 to 9 p.m. Thursday at the Thornridge Funeral Home, 15801 S. Cottage Grove, Dolton, and from 10:30 a.m. to an 11 a.m. Friday service at Spirit of God Fellowship Church, 16350 S. State, South Holland. Burial is in St. Casimir Cemetery, 4401 W. 111th.