An expert in defence strategy doubts drones will be enough to completely replace manned planes, in the Air Force.

Unmanned drones are being considered as a way of patrolling the country's coastal waters.

At the moment six Orion planes provide surveillance, but they're due to be retired in the mid-2020s.

Victoria University Professor Robert Ayson says unmanned drones could be useful for providing a quick look at things close to the coastline.

Mr Ayson says the drones could also be used to gather environmental information, such as oil spills.