Two men on his mess deck were playing around with it on their seemingly endless days at sea.

"I didn't even know anyone who ever played a guitar in my life - I was 16 years old and just left an industrial family in Yorkshire. And I said to these two blokes, 'Can you teach me a few chords'?

"I went and bought a cheap guitar and they taught me a few chords and when we went to sea we just played and sang."

Career and life got in the way, and he put the instrument aside. Ten years ago he picked up a guitar and fell in love all over again.

Now with the support of Soldier On, the veteran is spreading his love of music to other Canberra-based veterans and children in need.

For the past two years, he's been collecting donations of guitars and ukuleles, repairing them and giving them new owners.

So far about 120 guitars and 35 ukuleles have been donated to veterans and children.

In mid-2020, Mr Greef travelled to the South Coast with fellow Soldier On volunteer Mike Hogen to deliver refurbished guitars to children who had lost everything in the bushfires.

They gave away 42 guitars and 30 ukuleles, the small instruments being especially popular with children.

Another tour was organised just before Christmas, visiting small schools from Crookwell to Gundagai.

"Every time like we give a guitar or ukulele to these kids, it's just worth a million dollars. I just love it," he said.

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Perhaps more importantly, the project has given the veteran community a reason to gather and connect with each other every Thursday.

"The best thing I've found about it is it's just therapy, it really is," he said.

"And that's what I love about Soldier On, because there's a bunch of boys, we all get together there and play guitars and and have a chat.

"You can pick [the guitar] up at any time, any place, and just play it. Play it around for half an hour. I play mine, every single night because it's a good way to relax."

Mr Greef considers himself not badly affected by his time serving with peacekeeping forces in Cambodia during the transition years after the reign of Pol Pot.

For those who suffer post-traumatic stress disorder, the music sessions help bring a sense of purpose and community.

"It's just a matter of getting that veteran out of the house ... getting away from the fridge [with] their beer in it and giving them an interest."

He's hoping to push the idea further in 2021 by helping veterans in other states start similar programs collecting and donating guitars using the Soldier On network.

"I'm hoping, by the end of this year, I can have at least another four or five offices around Australia to do the guitar program the same as us, and try and make it nationwide."