He has reason to be upset. He recently lost touch with three asylum seekers he has been supporting for years, after they were taken the Bomana immigration centre, in Port Moresby.

It's part of the Bomana prison, and the men have been treated like inmates. Their phones have been confiscated and no one has heard from them.

One is suffering from acute intestinal and stomach problems. Another, Mr McKenna can't bring himself to speak about as he is a good friend.

How does a grandfather from inner south of Canberra become good mates with a man who has and will probably never set foot in Australia?

In the most unlikely of ways - through a nun at the Aboriginal tent embassy.

Sister Jane Keogh was staging a sit-in in front of Parliament House in the lead-up to Christmas 2015 to protest the treatment of people on Manus and Nauru.

The tent embassy had offered her sanctuary, as without it, she would not be allowed to stay in the Parliamentary Triangle.

Mr McKenna had worked with refugees through St Vincent de Paul since retiring from the army in 2002, and was part of a church group looking for ways to help more.

"I went and visited her there and we had a discussion. And I went back and visited her again and she said one of the things that bothered her was that it was relatively easy to get sympathy for the women and children on Nauru. But there were a bunch of guys on Manus who were essentially forgotten about by the community.

"She said what we should do is look for men on Manus no-one else is supporting."

So they began sending mobile phones. And buying phone credit.

At one point, their group Manus Lives Matter was looking after around 100 asylum seekers.

Then after sending parcels and phones "into a black hole" for nine months, Mr McKenna went to Manus in April 2017.

Over five days, he interviewed 20 men, all of whom were traumatised by their experiences on the island.

It was not long after they had been shot at by members of the PNG Defence Force.

Their situation has only deteriorated over Mr McKenna's last three visits.

He takes me through sheets and sheets of names and ailments. Kidney stones are an increasingly common complaint among the men of Manus, due to the poor food.

On his visit in January, the medical team brought an asylum seeker with kidney stones into the overcrowded Lorengau hospital one weekend.

The Australian government-funded Pacific International Hospital clinic is only open from 9am to 5pm on Mondays to Fridays, and on Saturday mornings, so any cases that require attention outside these hours have to present to the provincial hospital.

The man had to sleep on a bench in the waiting room, after his room was given to another asylum seeker, who'd tried to strangle himself.

Mr McKenna's friend Bill Gillespie was there as well. It was his first weekend in the country.

"Because it was 1pm [the clinic medical workers] just left him there with no care instructions. The hospital wasn't even equipped to provide aspirin for him so I went to the pharmacy and brought a big box of paracetamol and brought it up back up to the hospital, not only for the fellow left in the ER but for the hospital because they'd run out of medication," Mr Gillespie said.

Mr Gillespie isn't part of any of the refugee groups. He is at pains to point out to be he has no political affiliations either.

A Vietnam and Gulf War veteran "where the government lied to everyone", he wanted to see for himself what the conditions were like.

"It was really disheartening," Mr Gillespie said.

In the hospital in Port Moresby, he met a man who kept talking about self-immolating. The only radiography machine in the country is there, and it hasn't worked in three years.

"Even their own people dying of cancer, they can't care for them," Mr Gillespie said.

Canberra woman Sarah* - who has asked me to keep her identify secret so she does not get barred from visiting Papua New Guinea - said one of the asylum seekers she keeps in touch with was left worrying he had cancer for months because of the broken machine.

He was suffering from severe abdominal pain and vomiting but was unable to be transferred to Australia for a scan.

"I'd recently had bowel cancer and as soon as it was discovered, within two weeks I was having chemo and radiation," she said.

"For that man to be in that situation for months, worried he had cancer was extraordinary."

Sarah has been to the country 10 times on a tourist visa to see asylum seekers.

She befriended Kurdish-Iranian journalist Behrouz Boochani on Facebook, after reading some of his poetry online, and through him met others on Manus.

"It was a revelation to me that I could communicate with these people trapped in a remote detention centre," she said.

Some she speaks to daily, others weekly or monthly.

But it is hard to help them keep their spirits up.

"On my last trip over to Manus, I was at a conference a few days before where one speaker was talking about the concept of wise hope, not optimism where you really believe the outcome will be great, but where you know things might go wrong, it might not make a difference but you have to do it anyway. That's what it's like," she said.

For some of the asylum seekers, there is still hope they could be resettled in the US. For others, that path has already been closed and the future is uncertain.

For Mr McKenna, Medevac has helped alleviate their most desperate medical concerns. He just received a call from Port Moresby with the welcome news one man he has been advocating for will soon be transferred to Australia for treatment.

But how do you hold out hope in a hopeless situation?

"That's a tough question. I guess it's easy to despair but while there's life, there's hope. I guess I have faith in God and I have faith in Australians," Mr McKenna said.