Mr. Cosby’s exploits were detailed in his daughter’s 2010 book, “Quiet Hero: Secrets From My Father’s Past.” She wrote that her father left the family on Christmas 1983 and was largely estranged from her for more than 25 years.
In 2008, Rita Cosby discovered an old suitcase that had belonged to her father. It contained some of his World War II possessions, including his resistance armband and prisoner-of-war identification. She reached out to her father to reconnect.
Mr. Cosby told her that he had seen his home town destroyed by Nazi bombs and, still a teenager, lied about his age to join the resistance during the German occupation. He participated in the Warsaw uprising in 1944 and was eventually captured by German forces. He spent months in a Nazi prison camp and emerged weighing 90 pounds.
He escaped with a group of other prisoners in 1945. He told of hearing a plane above them and watching as the aircraft dropped what looked to be a bomb. Mr. Cosby leapt for cover. Afterward, he discovered the supposed ordnance was actually a parcel filled with chocolate bars and directions to the nearest U.S. forces.
After his liberation by the Americans in 1945, Mr. Cosby served in the Polish II Corps, an Allied unit. After the war, Mr. Cosby received a civil engineering degree from the University of London in 1954.
Two years later, he moved to the United States and lived for many years in Connecticut. He joined Mueser Rutledge in the early 1960s and retired from the consulting engineering firm in 1992.
Mr. Cosby moved to the Washington area in the mid-1980s. As an engineer with Mueser Rutledge, he worked on projects involving the National Gallery of Art, the Library of Congress and the Dirksen Senate Office Building.
In 2011, the Daughters of the American Revolution gave Mr. Cosby the Americanism medal, a prestigious award for naturalized citizens.
Mr. Cosby was born Ryszard Kossobudzki on Aug. 4, 1925, in Brzesc, Poland.
His first marriage, to the former Adda Arenfeldt, ended in divorce.
Survivors include his wife of 26 years, Judith Hoyt Cosby of Alexandria; two children from his first marriage, Alan Cosby of Greenwich, Conn., and Rita Cosby of New York; a son from his second marriage, Eric Cosby of Alexandria; and two grandchildren.