<P> The device could also be used as an underwater telegraph , sending Morse code through the water . The Fessenden underwater signalling apparatus , or more usually just `` The Fessenden '' , was fitted to Royal Navy submarines in World War I. British K - series submarines were equipped with Fessenden oscillators starting in 1915 . However , a submarine signalling the surface could be heard by any nearby ( enemy ) hydrophone , so the system had restricted utility during wartime patrols . </P>
<P> The device could also be used as an underwater telegraph , sending Morse code through the water . The Fessenden underwater signalling apparatus , or more usually just `` The Fessenden '' , was fitted to Royal Navy submarines in World War I. British K - series submarines were equipped with Fessenden oscillators starting in 1915 . However , a submarine signalling the surface could be heard by any nearby ( enemy ) hydrophone , so the system had restricted utility during wartime patrols . </P>
what sonar device let morse code messages be sent underwater from a submarine in 1915
what sonar device let morse code messages be sent underwater from a submarine in 1915
Fessenden
Fessenden