General Hurley acted in consultation with Employment Minister Eric Abetz to make the change, which effectively puts the sailors on a similar footing to military personnel fighting in battle.

The change, made on December 19, came as the government enacted its hardline election promise of turning back asylum-seeker boats, which critics have warned poses dangers to Navy personnel and asylum seekers. As many as six are believed to have been turned back to Indonesia in recent weeks.

It came as the Abbott government has announced the closure of four immigration detention centres, which Immigration Minister Scott Morrison said would save at least $88.8 million a year. The centres - Scherger facility in Queensland, Port Augusta facility in South Australia, Leonora facility in Western Australia and Pontville facility in Tasmania - were no longer needed, he said.

Also on Tuesday, refugee advocates said about 50 asylum seekers had gone on hunger strikes on Christmas Island and about six had sewn their lips together.

Activist Pamela Curr said the protests were largely over the separation of families in detention - a practice the government has denied is happening. A spokeswoman for Mr Morrison refused to comment, saying to do so could ''provide an incentive for such behaviour''.