On August 6th, 1945, an American bomber dropped the world's first atomic bomb over Hiroshima City. The entire city was devastated by the heat and shock waves of the blast, producing numerous civilian casualties.
In 1947, Hiroshima held a Peace Festival to promote lasting peace to people around the world.
World Peace Day Philippines Cover
A "World Peace Day" cachet was applied to the above cover cancelled at Manila on August 6, 1947. I do not know if the cachet was produced by the Philippines Bureau of Posts.