Yasuo Takamatsu, 57, grunts with the effort of hoisting a scuba diving tank onto his back, as he prepares to step into the cold waters off Japan's tsunami-ravaged coast to look for the body of his wife, one of thousands still missing three years on.

A swell lifts the wooden boat as he tugs on an over-sized rubber dry-suit that will protect him from the chill when he sinks into the murky, March-grey Pacific Ocean, just days before the anniversary of the disaster.

"She was a gentle and kind person," said Takamatsu. "She would always be next to me, physically and mentally. I miss her, I miss the big part of me that was her."

Takamatsu, a bus driver by trade, was never a natural candidate for learning to scuba dive and was worried he would not be able to do it.

But he feels driven to the water when he thinks about the last time he heard from his wife Yuko, before the nearly 20-metre (66-foot) wave engulfed her.

In a text message sent at 3.21 pm, half an hour after a huge undersea earthquake shook Japan on Friday, March 11, 2011 and unleashed a towering tsunami that travelled with the speed of a jet plane towards the Japanese coast, Yuko said simply: "I want to go home".

"That was the last message from her," he said.

"I feel terrible thinking she is still out there. I want to bring her home as soon as possible," he said.

Weeks later, while scouring the area, bank workers found Yuko's mobile phone and handed it back to Takamatsu.

He dried it off and fired it up to see that she had written a text message he had never received, at almost exactly the time the water was thought to have reached the roof of the bank.

"'Tsunami huge'. That was all she wrote in the very last one," he said.

Within minutes of the tsunami striking, communities were turned to matchwood, and whole families had drowned.

When the waves subsided and the water rushed back out to sea, it took homes, cars and the bodies of thousands of the people it had killed.

Officially, more than 15,800 are known to have died in the disaster, Japan's worst peacetime loss of life. Another 2,636 are listed as missing.

No-one thinks they will ever turn up alive, but for the bereaved, it is important to be able to find their bodies and finally lay them to rest.

More than 800 people were lost in the small fishing town of Onagawa alone, of whom more than 250 are still missing, including Takamatsu's wife, Yuko, then 47.

Minutes after the 9.0 magnitude earthquake, Yuko and a dozen of her colleagues at the local bank went up to the rooftop of the building, aware that a tsunami was rushing ashore.

- 'I felt my knees buckling' -

It was from there that she sent her last text message to her husband.

"It was about the time the tsunami went over the dock of Onagawa. I think the water reached the rooftop a few minutes later," Takamatsu said.

"I was not too worried after the quake because she was with her colleagues at the bank, although it bothered me that I couldn't contact her," he said.

Takamatsu was with his mother-in-law at a hospital in the next town when the sea came ashore.

He was not allowed to go back into the wrecked town, which was by then a seething, bobbing mass of buildings, fishing boats and cars, where pools of gasoline burned on the surface of the water.

When the barriers were lifted the next day, he rushed to Onagawa's hospital, which sits on a hilltop, as the designated evacuation site where hundreds had fled soon after the huge quake.

It was there that he learned the bank employees had been swept away.

"I felt my knees buckling. I felt nothing in my body."

Three years after the disaster, Japan is not officially prepared to give up the search for its missing.

Police, coastguard officers and volunteers have mobilised in their thousands to comb muddy areas around the mouths of rivers or to scour the seabed.

Search squads still recover some human remains.

Among the searchers is Takamatsu's instructor, Masayoshi Takahashi, who leads volunteer divers to look for the missing and clean the ocean floor.

Takahashi said he was happy to help his novice student and is keen to ensure he can learn to dive safely.

"During underwater search, unlike leisure diving, we have to dive in unclear water and there is also the risk of getting trapped in the wreckage," he said.

"I want him to become able to relax and look around carefully in water. He has a clear object to find."

Takamatsu knows that the chances of finding his wife are slim. In the three years since she died, swirling currents have carried all sorts of things across the Pacific; many others have sunk deep into the ocean.

But he knows that he cannot stop trying.

"I still feel just as I did when the disaster hit. Emotion-wise, I have not moved a bit since then," he said.

"I will feel like this, I think, until I find her. I do want to find her, but I also feel that she may never be discovered. The ocean is way too vast.

"But I have to keep looking."