text: Events leading up to J day, 1945. Spring/summer: Allies increased military pressure on Japan, bombing 60 cities and towns. large numbers were killed in the first attack on Tokyo. Plans for a land invasion of Japan were drawn up. 28th July: The Allies issued an ultimatum to Japan – the Potsdam Declaration – which was ignored. 6th & 9th August: The USA dropped atomic bombs on Hiroshima and Nagasaki, killing hundreds of thousands of people and causing long-lasting devastation. 8th August: The USSR declares war on Japan. 10th August: The Japanese government indicated it would sign the Potsdam Declaration. 15th August: Emperor Hirohito announced on the radio that Japan would accept the terms of Potsdam Declaration. 2nd September: The surrender is formally signed, ending WW2.