As Japan this week marks 79 years since the cities of Hiroshima and Nagasaki were destroyed by nuclear bombs at the end of World War II, Japanese officials have restated their aim to rid the world of atomic weapons. However, after decades of pacifism, the country is undergoing profound changes in its attitude to military power amid multiple regional threats – and is even seeking assurance that the United States would use its own nuclear deterrent to protect Japan. Henry Ridgwell reports from Tokyo.