A radical conservation group that has vowed to disrupt Japan's annual whale hunt launched its Antarctic campaign yesterday by renaming one of its ships after "Crocodile Hunter" Steve Irwin, the late environmental campaigner.

The US-based Sea Shepherd Conservation Society set sail from the southern Australian city of Melbourne vowing to use whatever means necessary to block Japan from harvesting up to 50 humpbacks, 935 minkes and 50 fin whales as part of an oceanic research program critics decry as commercial whaling in disguise.

Irwin's widow, Terri, threw her support behind the mission by giving Sea Shepherd permission to rename one of its two flagship vessels after her husband, the TV wildlife program host who died from a freak stingray attack off Australia's Great Barrier Reef in September 2006.