"I like the life experience and travelling the world, and not having to worry about paying off student loans for any future study," he said.
By contrast, Isaiah, 18, joined straight from high school, having wanted to join the RNZN since he was 16.
"I went to a Defence Careers roadshow when I was at high school a few years ago, plus some friends of my Dad were in the navy and they told us a lot of good stories.
"I liked that in the navy you get paid to do all this training, travelling the world, and getting posted to different ships."
They didn't see a lot of each other during the training - they were in different mess desks and different classes, but that will change in the foreseeable future. They have both embarked on Electrical Technician training.
"We have got a few tips from our Dad, who is an electrician, but I'm not sure how much that will count in our navy work."
For the two, the 5am starts and military naval methods took some adjusting to, and the brothers being on the same course led to some confusion.
"Like when there was a message for Recruit Panirau to report to the instructors' office, and we would both show up," Isaiah said.
However, overall the pair thrived.
"It was a steep learning curve in those first few weeks especially. "However, there are huge benefits from the discipline and leadership training in the navy, not just for the navy but for life outside too," Isaiah said.
Nathaniel said having structure and a good work ethic had really paid off for him – he lost 10kg during the course.
"If all of navy life is like Basic Common Training – surrounded by good people and working towards a common goal – then I look forward to the future," he said.
The brothers said their parents and whanau were very proud to have them both serving in the RNZN.
"Our family came up from Hawke's Bay for the Church Service at Devonport after our first six weeks of training and Mum and Dad were very happy.
"Mum had tears in her eyes, she was so proud," Isaiah said.
An NZDF spokesperson said the only other Royal New Zealand Navy siblings graduating together in the past five years were Wairoa brothers Kiwi and Vegas Tipoki.
They graduated in December 2017 and are currently together on HMNZS Canterbury.
The Panirau brothers will undertake trade training together at Devonport Naval Base.
However, after that there is no guarantee they will be posted to the same ship, although during their careers it is possible they will serve on the same ship at times.
