The Kaga helicopter carrier is not the biggest, fastest or most powerful warship to sail the seas, but its 500 crew wage a daily war on dirt and grime to keep it the cleanest.

At sunset each evening on a nine-day goodwill voyage from Indonesia to Sri Lanka, journalists watched the crew arm themselves with mops, brushes and dusters to clean the 248-meter-long Japanese ship.

"I believe that Kaga is the cleanest ship anywhere," said Hayato Nishida, a 36-year-old chief petty officer responsible for keeping the vessel spick and span.