The member - whose gender has not been revealed by the Navy - was part of a 21-strong crew on Cape Inscription.

The crew were pictured smiling and cutting a cake on the 58-metre Cape Class patrol boat just three weeks ago, when the order to "man ship" was issued for the first time.

At a naming ceremony in Perth on June 6, Executive Officer Lieutenant Joseph Woods said the small crew already had a strong bond.

"We are a closely knit team that mess together, exercise together and work hard together," Lieutenant Woods said.

The vessel, which has its home port in Cairns, was due to take part in border patrol operations with the crew in a 'month-on, month-off' rotation.

In a statement on Tuesday afternoon, the Australian Defence Force confirmed the Navy member's death "with deep regret".

"The member was deployed on Operation RESOLUTE in Australian Defence Vessel Cape Inscription," the ADF said.

"The next of kin have been informed and Defence is providing support to the member's family and shipmates.

"On behalf of the men and women of the Australian Defence Force, the Chief of the Defence Force extends his deepest sympathy to the family, friends and shipmates of the deceased member.

"Defence is liaising with local authorities and the cause of death is not yet known. As such, it is not appropriate to provide further details at this time."

Operation Resolute focuses on border protection, encompassing threats including "illegal maritime arrivals", piracy and illegal fishing.

Defence Minister Marise Payne acknowledged the member's death "with great sadness".

"The member was deployed on Operation Resolute, the Australian Defence Force's contribution to the whole-of-government effort to protect Australia's borders and offshore maritime interests," Ms Payne said.

"I extend my deepest sympathies and those of the Australian government to the member's family, colleagues and friends and I express my gratitude for the deceased member's service to our nation."