The U.S. Department of Defense has disclosed that South Korean, U.S. and Japanese submarine commanders jointly boarded an American nuclear ballistic missile submarine(SSBN) for the first time last month.

The Pentagon's Defense Visual Information Distribution Service(DVIDS) said on Thursday that the three officials visited a U.S. naval base in Guam on April 18 and boarded the USS Maine, an Ohio-class ballistic missile submarine.

The DVIDS also posted photos of the three commanders -- Rear Adm. Lee Su-youl, the commander of the South Korean Navy's Submarine Force, Rear Adm. Rick Seif, the commander of the U.S. Submarine Group Seven, and Vice Adm. Tateki Tawara, the commander of Japan's Fleet Submarine Force.

Seif reportedly said that this boarding reflects the special relationship between the three allies and the U.S. ironclad commitment to each alliance. The U.S. commander added that this strategic nuclear submarine is a highly efficient, reliable and decisive element of U.S. nuclear deterrence.

It is the first time that a Korean submarine commander has boarded a US SSBN in operation and also a first for submarine commanders from South Korea, the U.S. and Japan to jointly board such a vessel.