CANBERRA, June 6 (Xinhua) -- The Australian Defence Force (ADF) has failed to recruit enough sailors to put warships to sea, a report has revealed.

The "Cost of Defence" report, released by the Australian Strategic Policy Institute (ASPI) on Thursday, found that the ADF has failed to achieve "modest" recruitment goals contained in the 2016 Defence White Paper.

"Overall, it's only increased by 600 actual people against a target of around 1,730 over the period since the white paper," the report said.

"If increasing capital spending quickly is hard, increasing ADF numbers seems even harder."

As a result of the slow recruitment, one of the navy's upgraded Anzac class frigates has been stuck in a dry dock since 2017 because of a shortage of sailors.

"HMAS Perth, one of Navy's frigates, had gone through a very extensive refit and upgrade, got new radar capabilities, so a lot of investment went into that, but at the end of that process Navy couldn't find a crew for it," report author and former Department of Defence official Marcus Hellyer told the Australian Broadcasting Corporation (ABC).

"So, it's essentially sitting up on blocks for two years, out of the water because Navy doesn't have the people and I think that's really a microcosm of the challenges the defence force is facing.

"Defence is finding it really hard to recruit: it takes a long time to train a submarine captain or to train a fighter pilot - you can't just do that overnight."

The report did find, however, that military spending is on track to reach the government's goal of 2 percent of gross domestic product (GDP) by financial year 2019-20.

One of the ASPI's key recommendations was for the ADF to "devote more resources to autonomous systems" such as unmanned submarines and drones.

"One of the advantages of autonomous systems is less people, because these systems can do a lot of the job themselves," Hellyer said.

"Much of the cost of military platforms is due to the need to keep the crew alive, as is much of the complexity of design.

"Remove the crew, and the cost, risk and schedule needed to design and build the platforms decreases dramatically."