Prime Minister Tony Abbott says he hopes Darwin's four immigration detention centres will eventually sit empty.
On a visit to the Top End capital on Friday, Mr Abbott said his policy to stop asylum seeker boats will mean the facilities are no longer needed.
But he expects the centres will continue to be used for some time.
"We do not have these facilities to fill them up, we have these facilities to use at need," he said.
"I hope, I expect, within a relatively short space of time, our policies will have worked."
More than 1,000 people are being held at immigration detention centres in Darwin.
The Prime Minister was in the city to inspect a new Cape-class Customs patrol boat.
The vessels have a higher capability than the Bay-class vessels they are replacing.
Mr Abbott took a tour of Darwin Harbour on the Cape St George, the first of the new Cape-class Customs boats.
"In some ways [it is] a more capable vessel ... than the Armidale-class patrol boats deployed by the Navy," he said.
"It is about 100 tonnes bigger, it has a 4,000 nautical mile range, it has much more endurance."
The Prime Minister also said the Federal Government would provide the necessary funding to ensure the next rotation of US Marines in Darwin is effective.
More than 1,100 US Marines will arrive in the Top End in February next year in their biggest deployment yet to the Northern Territory.
Asked whether his Government would pay for the Marines' accommodation, Mr Abbott responded that it was important to ensure the rotations were properly catered for.
"Yes, we will do what is necessary to ensure that this rotation is as effective as possible," he said.
"One of the difficulties, I understand, under the former government is having agreed to the rotation it wasn't necessarily prepared to put the resources in to make it work.
"We will make this work."