The US military has experimented with its new self-driving warship.

The drone ship is designed to hunt for enemy submarines, and could be the next big step in robotic warfare.

The 40-metre-long unarmed prototype named ‘Sea Hunter’, can cruise the ocean’s surface for months at a time without no crew or need for remote control.

“This is an inflection point,” says Deputy US Defence Secretary Robert Work.

He said such ships could be operating in the western Pacific in just five years.

“This is the first time we've ever had a totally robotic, trans-oceanic-capable ship.”

The ship is projected to come with a $US20 million price tag each, and will cost $15,000 to $20,000 to operate per day.

That figure is very cheap for the US military.

Mr Work said it was possible that there would one day be weapons on the Sea Hunter, but maintained that any decision to use lethal force would be made by humans.

Elsewhere in the robo-vehicle game, six convoys of semi-automated “smart” trucks have arrived in the Netherlands after an experiment organisers say will revolutionise future road transport.

The array of self-driving trucks - by Europe’s six largest manufacturers - arrived in Rotterdam's harbour port in so-called “truck platoons”.

“Truck platooning” is when two or three trucks drive in an autonomous convoy connected via wireless technology.

The weekend’s arrival is the first-ever cross-border experiment using self-driving trucks, with rigs arriving from factories as far away as Sweden and southern Germany.

“Truck platooning will ensure cleaner and more efficient transport. Self-driving vehicles also contribute to road safety because most accidents are caused by human failure,” Dutch minister Melanie Schultz van Haegen said.

In the interests of safety, the semi-automated truck in the tests still had human drivers on board.

The people behind truck platooning say there are just a few hurdles that need to be ironed out before road users start seeing self-driving trucks.

“The next steps could be taken at an informal summit next week, which has been set up to discuss possible regulatory needs and changes to “make self-driving transport a reality”, Dutch officials said.