TheSDF director David Liddell said those results, together with findings from similar schemes in Europe, meant there was now "overwhelming" evidence in favour of having such a project.
In the first case in March 1999 theSDF chased two North Korean spy ships and fired warning shots after the ships were spotted off the Noto Peninsula in Ishikawa Prefecture.
This week theSDF and U.S. Navy and Air Force launched a massive 16-day joint exercise off the southern islands of Kyushu and Okinawa involving 47, 000 men (10, 000 Americans), 30 ships, a U.S. carrier, and 240 aircraft.