Submarine Sonar sound effect (echo sounder)?

Hi,

Am after a circuit that will recreate the sound of a submarine sonar(just like in those old naval war films). With the ability to vary the "send" sound echo & "return" sound blip time interval.

Can anyone help? They must have used some type of electronic circuit to mimic it for films, just need to know what it is.

Many thanks,

Mazz