The second atomic strike on the city of Nagasaki is less well known than the one a few days earlier on Hiroshima, but was it more influential in forcing the Japanese to surrender? To find out who exactly ordered it and why I talked to Harvard's Frederik Logevall. He discusses the debates that rage between historians as to whether Nagasaki was necessary and how much pressure there was for a third bomb. On the 75th anniversary of the strike it is a conversation with powerful contemporary echoes.