Like former battlefields all over the world, the southern Japan island of Okinawa - home to more than one million people and the site of some of the Second World War's most savage fighting - is a tinderbox of unexploded bombs, thousands and thousands of tonnes of them, rusted and often half buried.

The bombs are the bane of construction crews, divers and unsuspecting children. Because of their age and the layers of crusty dirt that usually cover them, they often don't seem dangerous.

A Japanese tourist recently was stopped at Okinawa's main airport for packing an old grenade he had found in his bags as a souvenir. In late January, a group of Okinawan children brought some bombs to show off at an elementary school, forcing teachers to evacuate the area and call in members of Nakano's military bomb squad. No one was injured.