A couple looking for a boat to buy online have opted for an unusual purchase - an ex-New Zealand warship.

Paul and Wilma Adams are now the proud owners the Royal New Zealand Navy dive tender Manawanui.

Mrs Adams said she felt "overwhelmed" to own such a prized item, which they will dock in Carrington, a suburb of Newcastle, 160km north of Sydney, according to the Daily Mail.

"What more can you ask for,'' she told the ABC.

Advertisement

"Paul (husband) looked regularly on websites to find a suitable ship and when he came out with it, it was like, 'hey darling, I've found the ship!'

"You can't find these in Kmart."

The Manawanui is purpose-built for diving sea missions.

Purchased for a "few hundred thousand dollars", the 44m long ship boasts a decompression chamber, a domed bell for deep diving and a crane for heavy lifting overboard.

The couple plan to use their prized asset to preserve fuel-laden vessels which sank in the South Pacific during the second world war.

Many of the wrecks are beginning to leak oil from the ocean floor.

The couple plan to lockguard the wrecks against leakage by using cathodic protection, with blocks lowered underwater from the Manawanui.

It has become a passion project for Mr Adams.

"Buying the ship was just the beginning," he said.

"There's a time bomb waiting to happen right through the Pacific.

"There's about 3000 wrecks out there. 300 of those were oil tankers. They are at the bottom of the ocean, and they are starting to leak."