Designed in 1937 by Giles Gilbert Scott, Waterloo Bridge across the River Thames was the last major reinforced concrete bridge built in the UK. The five-span, cantilever bridge has its haunched hollow-box beams faced in portland stone and, at 1250 feet, it's London's longest traffic crossing.

Construction coincided with the outbreak of World War II. Peter Mandell of Peter Lind and Company, the original contractor says, “Experienced construction workers were moved to the docks so women were brought in to work all along the river, including rebuilding Waterloo Bridge.” Despite damage from German bombers, this essential artery was completed in 1945 by the predominantly female workforce, earning it the affectionate name of “The Ladies Bridge.”

Christine Wall, an architectural historian, chanced upon the story but found no record of the women in official labor files. She is now making a documentary, “Concrete History,” highlighting the efforts of these and 24,000 other women employed in construction during the war.

However, Peter Mandell says there's no hidden agenda behind their unacknowledged achievements—the archive was simply lost when Lind temporarily suspended trading in the 1970s. “We're very proud of our female workforce,” he says. “We're rebuilding this archive and want to honor them with a plaque on the bridge.”

Waterloo Bridge's strategic importance meant it was not photographed during the war but the beginning of construction is captured in “A Window in London,” filmed there in 1939. —Elaine Saunders