The REMUS line of drone subs are used by the US navy to detect mines. They are low cost and can be operated from a single laptop.
The Swordfish is designed to carry out reconnaissance missions using sophisticated acoustic transponders to help it navigate.
Designed to scan the water for potential threats to other Navy vessels, the Kingfish is used by the US Navy to keeps their ports safe.
Developed by Rutgers University for the US Navy, the Naviator can both dive under water...
... and fly out of the water into the air.
The Dorado Seakeeper is an impressive looking unmanned submarine used by the Canadian Navy. That thing underneath it is a towable sonar, not a missile.
Shark drone! The GhostSwimmer is a US Navy submarine that looks and moves like a shark. The military have not released details about its intended use.
This drone is called Alister. But don't be fooled by the cute name, it was designed by the French to take part in mine warfare.
The Auv de SEcurité MARitime (ASEMAR ) is another French drone. It uses a state-of-the-art sonar to detect mines.
Made by Saab, the AUV62 Sapphires can perform a wide variety of tasks. It can hunt mines and even pretend to be a full-sized submarine, so real submarines can train by hunting it.
The Bluefin-21 is a popular unmanned sub that has already been used for some high-profile missions. One was used in the search for the wreckage of the missing Malaysia Airlines Flight 370. There's also a more military focused version of the drone — the Knifefish — but there are no publicly available pictures of it. The Knifefish weighs a huge 1,700 pounds (770 kg).
Here's an interesting one. A cameraman from Russian state TV, 'accidentally' caught these plans for a Russian drone sub on camera. According to the plans, the sub is designed to inflict radioactive contamination on enemy coastal targets.
Developed with a grant from the Department of Homeland Security, the BIOSwimmer mimics the motion of a tuna and is meant to be used for port security.
The Bluefin 9 can't dive very deep, but is designed to operate on extended mine detection missions.
The Double Eagle sounds cool and looks even cooler. Fitted with a disposal charge, it can take out mines with ease.
The Echo Range is a serious looking drone sub developed by Boeing for the US Navy. Eventually Boeing hopes that it will be able to stay under water for 70 days at a time...
..and here's it's big brother the huge Echo Seeker.
The HUGIN is used by the Norwegian and Finnish Navies. It can detect other submarines, mines and can take part in anti-submarine warfare.
