The families of Sub-Lieutenant Katsuhisa Ban and Petty Officer Mamoru Ashibe will probably never know for certain how or where they met their fate.

The Japanese midget submarine they commanded in a chaotic attack on Sydney Harbour on May 31, 1942 has finally been found and photographed, ending one mystery. But the remains of the two officers have not, leaving others unanswered.

Filled with sand and entangled in fishing nets from its 65 years on the ocean bed off Sydney's northern beaches, the midget sub M24 has now been declared a historic shipwreck.

Around its resting place 60 metres down and five kilometres off Bungan Head, a protected zone of 500 metres radius is now monitored by unprecedented security measures to keep it safe from interference or curious divers. Sonar alarm systems and underwater cameras record any vessel that stops within the exclusion zone and penalties of up to $1.1 million now apply for anyone caught disturbing the wreck and probable resting place of two Japanese war dead.

But the sensitivity of the site - which cannot be excavated - means some mysteries will endure. We may never know why the submarine ended up where it did, given its planned rendezvous with a mother vessel near Port Hacking. We will never know for certain whether Ban and Ashibe died inside, although the position of the exit ladder and other clues suggest they did, said Lieutenant-Commander Etienne Mulder of the navy.

Elite navy clearance divers yesterday collected a jar of sand from the ocean floor beside the submarine to be delivered to the officers' families.

False reports of the sub's discovery had numbered in the hundreds since the three subs attacked Sydney Harbour. One became entangled in a net across the harbour mouth, where it was discovered by a man in a row boat and depth-charged after much discussion and double-checking. The second made it into Taylors Bay near Taronga Zoo before coming under attack. But the third made it almost as far as the Harbour Bridge before turning around and torpedoing the navy depot vessel Kuttabul at Garden Island, killing 19 Australian and two British sailors. It then disappeared and was not seen again until last year.

Historic sub's secrets to remain protected … by sonar - National

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