In all, about 12,000 American prisoners of war were put into forced labor by the Japanese government and private companies seeking to fill a wartime labor shortage, of whom more than 1,100 died, said Rabbi Abraham Cooper, an associate dean at the Simon Wiesenthal Center.
Six prisoner-of-war camps in Japan were linked to the Mitsubishi conglomerate during the war, and they held 2,041 prisoners, more than 1,000 of whom were American, according to nonprofit research center Asia Policy Point.
Mitsubishi Materials' predecessor ran four sites that at the time of liberation in 1945 held about 876 American prisoners of war. Twenty-seven Americans died in those camps, Asia Policy Point said.
While previous Japanese prime ministers have apologized for Japan's aggression during World War II, private corporations have been less contrite.
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On Sunday, Kimura was flanked by Yukio Okamoto, a forced laborer in a copper mine and a special advisor to Japanese Prime Minister Shinzo Abe, along with an image of American and Japanese flags.
In the audience were other forced labor survivors and family members.
"This is a glorious day," said 94-year-old veteran James Murphy, who survived working at Mitsubishi Mining's Osarizawa Copper Mine and the infamous Bataan Death March in the Philippines. "For 70 years we wanted this."
The apology comes near the 70th anniversary of the end of the war.
It also comes amid a lawsuit in which the descendants of hundreds of Chinese men forced to work in wartime Japan are seeking millions of dollars in compensation from a subsidiary of Mitsubishi and a joint venture between Mitsubishi and Mitsubishi Materials.
Kimura declined to discuss the lawsuit. He also declined to discuss whether the apology would be echoed by other companies that benefited from the labor of captured soldiers.