Aussie puzzles out midget sub mystery

SYDNEY (Kyodo) An Australian government maritime archaeologist appears to have partially unraveled the mystery of how a Japanese midget submarine that attacked Sydney Harbor during World War II finally met its end.

Tim Smith, who led an official investigation of the M24 after its discovery off Australia's east coast in November 2006, believes he has found the answer to where the Japanese two-man submarine M24 was heading during its final hours.

After lying undisturbed on the ocean floor for almost 65 years, the submarine was discovered by a group of amateur divers.

The discovery helped bring a sense of closure to family members of the Japanese submariners — 23-year-old Sub-Lt. 1st Class Katsuhisa Ban, the sub's commander, and 24-year-old Petty Officer 1st Class Mamoru Ashibe, the navigator — whose remains are thought to be still resting in the underwater grave.

But for WWII historians, the find threw up more questions than answers.

The location of the sub, found to the north of Sydney Harbor, was puzzling and unexpected.

The experts had long assumed the M24 had fled south of the harbor to Port Hacking, where a rendezvous point had been arranged with the main fleet of Japanese mother submarines.

However, after scuttling an Australian navy barracks ship and killing 21 Allied sailors, the M24 fled in the opposite direction and eventually sank 11 km north of the harbor.

Two other midget submarines that accompanied the M24 on the May 31, 1942, raid were blown up in the harbor and sank without inflicting any Allied losses.

After examining maps recovered from the two other subs and records of Japanese telegraphic orders, Smith said there was a second rendezvous point planned for the midget sub, 20 km north of the harbor near Broken Bay.

"The records show the Japanese had more flexibility in their recovery plans than previously thought," Smith said.

The final resting place of the M24 lies almost exactly along the route toward Broken Bay and about halfway toward the rendezvous point, he said.

"There is no doubt the northern rendezvous point is where Ban and Ashibe were heading," Smith said.

"The crews were probably trained to act more independently when they came out of the raid and go to a place that suited them, based on their situation, weather conditions, and if they were being observed or followed."

Ban and Ashibe had probably made the tactical decision to head to the northern meeting point because the M24's torpedo attacks had put the Australian forces on high alert, and they did not want to lead the navy to the Japanese mother submarines, Smith said.

There are several likely scenarios on what finally grounded the M24 halfway to its meeting point.

"They could have simply run out of battery power, or maybe they were overcome by bad air (lack of oxygen or excessive fumes), or decided to commit suicide and end the mission," Smith said.

An analysis of the M24's access ladder showed the pair did not attempt to escape from the sub, he said.

It is unlikely any further information will be revealed about the final hours of Ban and Ashibe unless the wreckage is brought to the surface.

The state government of New South Wales plans to leave the sub and the remains of Ban and Ashibe undisturbed.

The site is being protected by a legislated 500-meter exclusion zone and heritage listing. Any divers who breach the exclusion zone face fines of up to 1.1 million Australian dollars (¥100 million).

Meanwhile, the sturdy steel grave of Ban and Ashibe is in good condition despite having been more than 65 years underwater, and is likely to remain intact in its final resting place for several hundred years to come, Smith said.