The crew of the HMNZS Manawanui didn't realise autopilot was engaged as it crashed into a Samoan reef, a military Court of Inquiry has found.
New Zealand's worst peacetime maritime accident occurred in October when the ship sunk off the coast in bad weather, with all 75 crew making it to shore in a dangerous overnight evacuation.
Chief of Navy Rear Admiral Garin Golding ordered the probe, which found a "series of human errors" behind the $NZ147 million ($A133 million) ship's loss.
"The crew did not realise Manawanui remained in autopilot and, as a consequence, mistakenly believed its failure to respond to direction changes was the result of a thruster control failure," Rear Amdl Golding said.
"Having mistakenly assessed a thruster control failure, standard procedures should have prompted ship's crew to check that the ship was under manual control rather than in autopilot.
"This check did not occur. Remaining in autopilot resulted in the ship maintaining a course toward land, until grounding and eventually stranding."
The finding is part of a preliminary report into the matter, with the Court of Inquiry to continue into 2025.
The vessel ran aground on October 5 while undertaking surveying work, with Commander Yvonne Gray, the ship's captain, ordering an evacuation half an hour later.
It took around five hours for the crew to make it to shore in life rafts and inflatable boats, assisted by local seafaring Samoans who became aware of the distress.
The ship caught fire and sank early on the morning of October 6.
Rear Adml Golding said he took responsibility for the crash, and he had ordered audits across the navy fleet of eight vessels.
NZ's naval forces were already under intense pressure, with attrition grounding up to four of the ships in recent times, and government-ordered belt-tightening.
The blunder prompted Prime Minister Chris Luxon to apologise to Samoa, New Zealand's former colony which it has a history of mistreating, and organise a salvage operation.
