Vandals have damaged the wreck of a Japanese mini submarine that famously attacked Sydney Harbour during World War II, stealing parts and protected relics, authorities said on Thursday.
The crews from two of the three vessels involved in the assault scuttled their boats and committed suicide but the fate of the third was unknown until 2006 when scuba divers discovered it off Sydney's northern beaches.
Authorities put an exclusion zone around the vessel, which is believed to contain the remains of the two crew members and personal items such as samurai swords and good luck charms. It is supposedly monitored by long-range cameras.
But divers entered the site, damaged the hull of the midget submarine and stole relics, Australia's Environment Department said in an appeal for information, without specifying what had been taken.
"The resulting damage includes the breaking off and removal of two of three visible propeller blades... of the submarine, causing permanent damage to a significant piece of Australia's WWII heritage," the department said.
The damage was discovered during an archaeological inspection.
Anyone found guilty of damaging or disturbing a protected wreck faces up to five years in jail. The site is also protected under New South Wales heritage laws, with a breach incurring a fine of up to Aus$1.1 million (US$1.14 million).
The lethal assault in 1942 came after a Japanese reconnaissance flight reported Allied warships anchored in Sydney Harbour.
The commanding officer of a flotilla of five Japanese large submarines cruising off the city decided to attack with three mini submarines, each carrying a two-man crew.
They avoided the partially constructed Sydney Harbour anti-submarine boom net and attempted to sink the warships but were detected and attacked.
One submarine attempted to torpedo the heavy cruiser USS Chicago, but instead sank the converted Australian ferry HMAS Kuttabul, killing 21 sailors.