Simplify the following text for a Grade 9 native English-speaking person.
Original: On 15 August 1945 Japan surrendered , with the surrender documents finally signed aboard the deck of the American battleship USS Missouri on 2 September 1945 , ending the war .
Simplified: On August 15 , Japan formally surrendered to the Allies . The surrender documents were signed formally on board of USS Missouri on September 2 , 1945 , ending the war .