A series of futuristic-looking, remote-controlled water vehicles could be added to the Royal Navy's arsenal.
The drones can be operated from a distance by humans
The Ministry of Defence has commissioned a £200,000 study of a group of drones.
These include a robot patrol dinghy and a small aerial drone, similar to a seaplane, which is designed to take off and land on water.
The machines will be subjected to testing at sea by naval experts over the next three years.
One of the vessels being considered is a carbon fibre mini-submarine capable of being programmed by satellite and used to conduct covert surveillance.
Another vehicle is almost completely submerged, with a single spar protruding vertically above water which carries radio and positioning equipment.
One larger boat is capable of carrying machine guns and missiles, as well as cameras and radar systems, and is designed to investigate suspicious craft or objects as the operator remains at a safe distance.
A spokesman for the Defence Procurement Agency said: "These machines could be very useful in doing dull, repetitive jobs where we can put resources elsewhere.
"But the key thing is they could be used in dangerous situations where we may not need to put lives at risk."
Defence Procurement Minister Lord Drayson said government strategy aims to ensure that the UK armed forces are at the "cutting edge".
Some of the vehicles can operate under water
He said: "Unmanned surface vehicles are going to be very important for the Royal Navy in the future and these trials, carried out in partnership with industry, will allow us to explore their future potential."
The MoD said they could be used in conjunction with warships to extend their range and move into battlefields without putting sailors at risk.
Unmanned vehicles, on the ground and in the air, play an increasingly important role in modern warfare.
The US government has said the MoD is in the process of buying two unmanned Predator aerial drones at a cost of up to £40m.
The drones, which are widely used by the US military, are capable of carrying Hellfire missiles and laser-guided bombs.
It is believed that they will be brought into service in Afghanistan where some British Army soldiers have complained of the lack of air support.