Activists aiming to halt Japan\'s whaling fleet Tuesday revealed their new weapon for their latest Antarctic campaign -- a US$2 million ship once owned by the government in Tokyo. Lockhart MacLean, captain of the renamed Sam Simon, said the militant Sea Shepherd Conservation Society was able to buy the vessel after a US company, New Atlantis, purchased it when it was advertised for sale. \"It\'s a Japanese vessel,\" MacLean told AFP, adding that it was ideal for chasing the harpoonists through the freezing and remote waters of Antarctica where they annually hunt for whales during the southern hemisphere summer. Japan says the hunt does not breach an international moratorium on commercial whaling because it is done in the name of \"scientific research\" but the meat is later sold openly in shops and restaurants. The new Sea Shepherd vessel was built as a scientific observation ship and run by Japan\'s meteorological agency until 2010. \"Her main career was doing that, collecting ocean current data, weather observations, that sort of thing,\" MacLean said from Hobart in Tasmania, where the boat was being launched on Tuesday. \"It\'s interesting that it was actually a real research ship, whereas we feel that Japan is not doing any significant research down in Antarctica. We actually own a real Japanese research ship. \"I guess it\'s ironic in that sense.\" Sea Shepherd has said that this year\'s campaign against the whalers, its ninth, is its biggest ever, but until now it had kept the identity and location of the Sam Simon a secret. MacLean said the 56-metre (185-foot) boat was in good condition, had a thick, strengthened hull suitable for icy conditions and could keep up with the whalers for 60 days -- about two-thirds of the expected Antarctic campaign. \"The vessel will be able to keep up with the Japanese factory whaling ship. That was the main criteria that we needed,\" he added. Sea Shepherd bought the ship after a donation from Sam Simon, the American television producer best known for \"The Simpsons\", and renamed it in his honour. MacLean said Simon himself was expected to be part of the Sea Shepherd campaign this year, travelling on the flagship vessel the Steve Irwin, which is already at sea and skippered by controversial Sea Shepherd founder Paul Watson. The group, whose vessels harass the Japanese fleet to prevent them slaughtering whales, has four ships, a helicopter, three drones and more than 100 crew members in Operation Zero Tolerance.