Sailors hold back tears as Darwin departs

Sailors have squeezed back tears in an emotional farewell with family and friends at the departure of HMAS Darwin for a six-month deployment to the Middle East.

The ship's company of 229 sailors and officers marched on to the 4000-tonne warship and set off from Sydney on Wednesday, waving goodbye to wives, husbands, children, family and friends.

HMAS Darwin has been sent to combat piracy, smugglers and terrorism in its seventh deployment to the region.

Prime Minister Malcolm Turnbull said it was "a mission of critical importance to Australia and international security".

"Go with the thanks of the Australian people," he said at the farewell ceremony.

Commanding Officer Phillip Henry told reporters the objective of the mission was to contribute to the region's security and disrupt drug syndicates.

"It's absolutely important...it interrupts the funding line for terrorism," he said.

He said leaving behind his wife and four children never gets easier, despite his many deployments.

Sailor David Gouge, 28, fought back tears as his eight-year-old son Riley wrapped his arms around the father's neck and clung to their final moments together for a while.

"Feeling quite overwhelmed but we are feeling prepared," Mr Gouge told AAP.