TOKYO - A Japanese Maritime Self-Defense Force "helicopter carrier" set sail to escort a US Navy vessel in the Pacific, marking the first time such a protection mission has taken place under the controversial new security legislation.

Japan's Ministry of Defense said the inaugural mission, since contentious new legislation took effect last year, is aimed at showing that the Japan-US alliance stands firm amid rising tensions on the Korean Peninsula.

The security legislation, which has looser, ambiguous constraints imposed on Japanese forces by Japan's war-renouncing Constitution, allows SDF members to escort and guard vessels and weapons that belong to US forces.

This protection mission, ordered by Defense Minister Tomomi Inada, came as the two countries may be engaged in joint exercises or the monitoring and information-gathering activities related to missile launches by the Democratic People's Republic of Korea.

The Izumo helicopter carrier is the largest warship Japan has entered into service since World War II. Clearly a de facto aircraft carrier as military analysts have attested, it left the Yokosuka base, south of Tokyo, on Monday morning.

The USS Carl Vinson aircraft carrier strike group and MSDF vessels entered the Sea of Japan off the Korean Peninsula on Saturday to carry out joint exercises, ministry officials here confirmed.

The latest actions of the ministry and the MSDF in particular deploying hardware and personnel into regions where there might be conflicts threaten to invalidate Japan's pacifist Constitution.

The Constitution states that the Japanese people "forever renounce war" and ban the "use of force as a means of settling international disputes". It also states that "land, sea, and air forces, as well as other war potential, will never be maintained".

Xinhua