A specialist team of deep-sea experts endured the effects of a tropical cyclone, conducted hours of painstaking research, but also had some extraordinarily good luck before finally solving one of Australia's greatest naval mysteries; finding the final resting place of the sunken Montevideo Maru.
On Saturday the Silentworld Foundation announced it had located the wreckage of the stricken Japanese POW transport ship, more than 80 years after it was mistakenly torpedoed by a US submarine in the South China Sea.
The long-awaited discovery just before Anzac Day closes a chapter on the worst maritime disaster in this country's history, in which approximately 1,060 World War II prisoners died, including about 980 Australian troops and civilians.
A 33-year navy veteran and submariner, who until recently led the Australian Defence Force's undersea capability, described to the ABC the painstaking work leading up to the successful operation, which took place 4,000 metres below the ocean's surface.
"Planning for the mission began many years ago, but work began ramping up in earnest in the last couple of years," retired Commodore Tim Brown explained.
"Silentworld Founder John Mullen assembled the search team of undersea and exploration experts to work alongside members of the Montevideo Maru Association. These individuals' singular focus was finding the Montevideo Maru.
"This team painstakingly trawled through countless records across the USA, Australia and Japan to produce a solid plan upon which to base a successful search and gain the government's and Defence's support.
"The key was assessing the exact location of the Montevideo Maru based on the historic records of the USS Sturgeon, which tragically sunk the SS Montevideo Maru at night, unaware it was carrying prisoners of war en route to Hainan Island."
The team were able to map out a "relatively large search area" where they had a high degree of confidence the WWII shipwreck would be located.
Eventually on April 1 this small specialist team, with the help of Dutch deep-sea survey company Fugro, set out on an expedition to find the wreck in the depths of the South China Sea, north-west of Luzon.
Working around the clock on two separate "watches", the crew used cutting-edge technology on the ship to first carefully map the ocean floor to prepare for the next stage of the mission.
They then deployed Fugro's advanced unmanned underwater vehicle that carried both a multi-beam echo sounder and high-fidelity side scan sonar and sent it on its pre-programmed search pattern, flying 100 metres off the ocean floor and operating at depths in excess of 4,000 meters.
"Fortunately for us, we found the ocean floor in that region is sparse and flat — perfect for seeing a wreck. Technology, planning, mother nature and time combined to enable this search to be successful," Commodore Brown said.
"We had to set the autonomous underwater vehicle (AUV) at 100 metres above the ocean floor to begin with, to ensure we could cover the entire search area.
"We actually wanted to start closer to the bottom to maximise the opportunity to see a contract of interest, but this would have reduced the overall search area, so a compromise had to be found.
"Each run took about 40 hours before we had to recover the AUV back to our ship. We then processed terabytes of data, which took may hours, before pictures would start to emerge on the screens.
"Each time one could feel the tension biting at everyone in the operations room."
Speaking to the ABC from the survey vessel still in the South China Sea, Commodore Brown described how "the undersea environment is heavily shrouded in opaqueness".
"It takes a huge investment in people, time, and capability to see what lurks below the surface. The Fugro technology is leading edge, but it still takes a huge effort by many people to pull it all together," he said.
The 12-day mission was also hampered by heavy weather caused by a small cyclone near the Philippines, which made it temporarily impossible to operate the sensitive deep-sea equipment, so the team briefly paused their activity to reassess and refine the search area.
Then, as the team neared the end of completing a sweep of their third survey area, the AUV happened to pass over the Montevideo Maru wreckage.
Commodore Brown recalled how it was "clear on first inspection. We immediately sensed we had found it—it just looked right".
"We knew it, but we had to spend several more days proving it to ourselves," he said.
"The world's now seen the high-fidelity pictures of the wrecked Montevideo Maru, which entombs so many lost souls in the silence of the deep ocean.
"These detailed and ghostly images took multiple runs of the AUV running over the wreck at about 45 metres off the ocean floor.
"It was amazing. Twenty years ago you couldn't have done this. The technology simply didn't exist."
