Crew members aboard a Maritime Self-Defense Force warship may have been repeatedly drinking alcohol outside authorized hours during their deployment to the Indian Ocean, it was learned Thursday.

The drinking took place aboard the destroyer Harusame, part of a task force providing logistic support to the U.S.-led military campaign in Afghanistan, according to sources close to the MSDF.

Last year, it was discovered that unauthorized drinking took place aboard the destroyer Asakaze, which was also sent on the mission, leading to reprimands for 25 service members, including the ship's skipper and the commander of the Fourth Escort Flotilla.

According to the sources, "several dozen" crew members are suspected of the rules violation aboard the Harusame, and an investigative committee has been set up to probe the matter and dole out punishment, if deemed necessary.

The Harusame, with a complement of 165, left Japan in November and returned to its home port of Yokosuka, Kanagawa Prefecture, on May 20 after its stint in the Indian Ocean helping to refuel foreign vessels.

In principle, drinking on board is permitted only between sundown and 10 p.m., and times when the vessel is in port. Even in such cases, authorization must be granted from the chief of staff of the MSDF. The rules were beefed up in January after the Asakaze incident.

According to the sources, alcoholic beverages were sold in the Harusame's onboard concession when it was docked at a port on the Arabian Sea. It is believed the beverages bought at this time were consumed even after lights out.

The MSDF has sent 23 vessels to the Indian Ocean for the antiterror campaign since November 2001, and has provided 307,000 kiloliters of fuel to warships from 10 countries, according to the Defense Agency.