PERTH, Australia (AP) — He speaks with a calm, steady voice as he tackles question after question in an attempt to explain one of the biggest mysteries the modern world has ever known: What happened to Malaysia Airlines Flight 370?

Angus Houston has become the global face of the massive monthlong search operation off Australia’s west coast to find the missing Boeing 777, which is believed to be resting on the silt-covered bottom of the southern Indian Ocean, somewhere in a patch of sea the size of Los Angeles.

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The lanky former head of Australia’s defense force has been praised for restoring credibility and confidence that was missing early on when Malaysian officials were tasked with providing answers about how and why the jet carrying 239 people could have flown so far off course and vanished.

Once satellite data revealed that the plane was last detected off Australia’s coast, the search — along with the responsibility of updating the world — fell on Houston.

As head of the joint agency coordinating the search, Houston has said from the get-go that he has nothing to hide, and has promised to release every detail of the slow-moving hunt to the passengers’ families, who are desperate for any pinch of new information that could explain why their loved ones took off in Kuala Lumpur, Malaysia, on March 8 but never landed in Beijing.

Houston, 66, has a history of taking care of grieving families, including writing letters to air force pilots’ widows. Australians know him as a military man with a heart.

“He’s accepted to be an exceptionally professional officer and a very personable one, and a deeply caring person,” said Neil James, executive director of the Australian Defense Association security think tank, who’s known Houston for years. “A lot of senior military officers have a much colder exterior. They’re not always known to be deeply caring, but Houston actually was.”

Houston is now a well-known face among Australians, but he didn’t start out here. Born in Scotland, he moved Down Under when he was just a young man, working for a stint as a jackaroo, or farm hand, at a cattle station. He later joined the Royal Australian Air Force — where his given name, Allan, was replaced by the nickname Angus because of his strong Scottish accent, which has long since disappeared. He went on to become a decorated helicopter pilot, after being initially told that at nearly 2 meters (6-foot-5), he was too tall to fly fighter jets.

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He worked his way up through the ranks, first serving as the air force chief before becoming head of the defense force, where he oversaw military operations in East Timor, Iraq and Afghanistan.

When Houston retired from that position in 2011 after six years on the job, then-Prime Minister Julia Gillard surprised many when she gushed about him to his wife at a farewell event. “Every woman I know is a little bit in love with your husband,” she said. “I’m a little bit in love with your husband.”

His high-level military experience means Houston is no stranger to leaders in China and Malaysia, who are following every step of the search for the missing aircraft just as closely as he is. He refuses to speculate or put too much weight on the potential that any new lead could bring. Instead, he repeatedly warns that the search for an airplane in a vast, largely unexplored area about 4,500 meters (15,000 feet) down on the ocean floor is a major undertaking, and has stressed that there are no guarantees the jet will be found.

“I’ve watched him on the news ... and he definitely has more credibility than Malaysia Airlines and the Malaysian government,” said Wang Chunjiang, whose younger brother was aboard the plane. “The Chinese families really appreciate Australia for their efforts in the search. It isn’t their flight, and yet they’re really trying their best to do it.”

Despite the exhaustive search for Flight 370, not one sliver of debris has been found to indicate where the plane, which was carrying mainly Chinese passengers, might have ended up. Wrong information and misleading messages from Malaysian authorities have lifted the hopes of the passengers’ relatives, left them confused or made them downright angry. Some Chinese families, waiting to hear news about their loved ones, have accused authorities of bungling the investigation, lying about information or even possibly participating in a cover-up involving the plane’s disappearance.

Malaysia initially said it couldn’t release all of the details it had about the flight, prompting suspicion. Then it took about a week to reveal why search crews were sent far west of where the last contact with the plane was made, explaining that radar had detected it there. Even the last words spoken from the cockpit were revised more than two weeks after being released.

Since taking over as head of the search, Houston has managed to create a sense of order.

“He exudes more confidence,” said Lim Kit Siang, a veteran Malaysian opposition leader. “People trust him because he is seen as authoritative and he hasn’t been plagued by contradictions, confusions or retractions of statements.”

But the Australian-led search operation hasn’t come without criticism. Media access has been greatly curtailed, compared to more openness in Malaysia, and the message is carefully managed, frustrating hordes of journalists who have camped out for weeks in Perth, on Australia’s southwest coast.

Analysis of satellite data led officials to believe the plane veered off course — for reasons that remain a mystery — and flew until it ran out of fuel over a largely unmapped, giant swath of unruly sea.

Throughout the six-week search, hope has soared and sputtered repeatedly, with possible leads ranging from oil slicks to debris floating in the water. Nothing has panned out, but the best shot came when underwater electronic signals were picked up by an Australian ship towing a listening device that can detect pings from the plane’s all-important black boxes.

Four transmissions were picked up on April 5 and 8, and Houston has expressed cautious optimism that the sounds had indeed come from the plane’s flight data and cockpit voice recorders’ beacons just before their batteries died.

A robotic submarine has now assumed the arduous task of scouring a vast patch of ocean floor that is still largely a mystery itself. The sub is using sonar to map out a potential debris field, but after five dives this week covering more than 110 square kilometers (42 square miles), it has come up empty.

This “is one of the largest search and rescue, search and recovery operations that I’ve seen in my lifetime,” Houston told reporters this week. “We’ve got to be realistic about this. It may be very difficult to find something, and you don’t know how good any lead is until you get your eyes on the wreckage.”

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Associated Press writer Eileen Ng in Kuala Lumpur, Malaysia, and news assistant Fu Ting in Shanghai contributed to this report.

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Follow Margie Mason on Twitter at twitter.com/MargieMasonAP