Defence was asked about any sensitivities over Darwin's China port deal, the NT Government says.

Defence was consulted prior to the deal being sealed, after a NT parliamentary committee noted the strategic position of the port and warned no foreign investment should occur that threatened the country's security interests.

While a Federal Government spokesperson said Defence secured a 15-year access agreement to the port in anticipation of the lease occurring - they also said it was spending millions of dollars on an alternative barge facility in Darwin.

The Maritime Union of Australia (MUA), which is against the deal, has labelled the lease a strategic worry for the Top End, which plays host to a large Australian Defence presence and yearly rotations of USA Marines.

The USA Chief of naval operations, Admiral Greenert, when he was in Australia last year clearly identified port infrastructure needs in Darwin as a critical element to the growth of 'cooperation' in Darwin.

Parliament has approved an $18 million project to build a barge facility at a site adjacent to the Darwin port that will be capable of loading and unloading giant amphibious naval ships at short notice.