"My greatest enjoyment is seeing a 12 or 13-year-old coming through as a scared little kid, and then going out as a confident 18-year-old," he said.
A Territorial Force member for 20 years and a mechanic by trade, he had just returned from Australia in 1994 when former unit committee chairman Bill Donnithorne asked him to join the unit.
He originally declined, but the next year in 1995 ended up joining the committee as a civilian before becoming an officer in 1998.
His first stint as unit commander lasted for 12 years until he stepped down from the unpaid, voluntary role four years ago, before returning to the position in 2016.
"I was a reluctant recruit. I didn't want to become involved originally, but once I did, I gave it 120 per cent."
With the help of a "very good" committee and "fantastic support" from NZ Cadet Corps headquarters at Ohakea, Major Chapman was proud of the Ruahine Cadet Unit's achievements during his time.
"It's a good-sized unit, and probably in the top three units in the country.
"It's won the Best in New Zealand trophy three times, the Best in Central Region trophy seven times, and the national skills title once. They are probably my three crowning achievements."
He was also proud of helping establish the Napier Cadet Unit and said 30 CHB cadets had gone on to join the armed forces during his tenure.
Formed in 1991, the Ruahine Cadet Unit, part of the New Zealand Cadet Corps, is a voluntary military-style youth organisation which teaches leadership, comradeship, self-confidence and citizenship to boys and girls aged between 13 and 18.
Together with the Sea Cadet Corps and the Air Training Corps, the Cadet Corps make up the New Zealand Cadet Forces, which were established under the Defence Act 1971.
During their three years with the unit, cadets rise up the ranks as they successfully complete training in shooting, map reading, bush craft and survival skills among other areas, earning up to 80 credits towards their NCEA levels in the process.
Along with performing official duties at Anzac Day services and citizenship ceremonies, cadets also learned the benefits of doing a "huge amount" of work in the community, Major Chapman said.
"I've tried to teach them self respect, self pride and to be proud of who they are. That's my philosophy in life.
"And that shines through at the end of the day when they walk out proud and upright and very respectful of their elders."
He'd only had four or five youngsters "go off the rails" in his time, which was pretty good considering the timespan.
Overall, his time with the unit had been a spectacular ride, he said.
"The whole 22 years has been brilliant."
Waipukurau and Districts RSA president and chairwoman of the Ruahine Cadet Unit support committee Janet Castell thanked Major Chapman for his dedication.
"There have been times over the years that if it was not for Major Chapman and his dedication to the Ruahine Cadets, the unit would have faltered and a number of young people would have missed out on what is a great experience."