FL-boat
The FL-boat (Fernlenkboot, literally "remote controlled boat") was a weapon used by the Imperial German Navy during World War I. It was a remote-controlled motorboat, 17 m long, carrying  of explosives, which was intended to be steered directly at its targets - initially the Royal Navy monitors operating off the coast of Flanders.

FL-boats were constructed by Siemens-Schuckertwerke.  They were driven by internal combustion engines and controlled remotely from a shore station through spooled wire unwound behind the boat. The wire was  long and the spool weighed . An aircraft could be used to signal directions to the shore station by radio. The commands available to the boat operator were:

 System test
 Engine start, engine stop
 Set Rudder position
 Turn on a light, to enable the boat to be tracked at night
 Detonate the warhead, to prevent capture of the boat if it missed its target

Planned developments were to use a control station carried on a ship, in an airship or use a radio-control system. The boats could attain speeds of .

On 1 March 1917 an FL-boat hit the Nieuwpoort mole and on 28 October 1917 one hit the Royal Navy monitor HMS Erebus.