Want this question answered?
ASDIC
It's called the rudder
Sonar SOund Navigation And Ranging
a divice that supplies air to underwater swimmers
The Piranah Water 3000
You wouldn't need a scientist of any particular specialty to build a device.
it measures the depth under water
Assuming you mean Jacques Yves Cousteau - he invented the Self-Contained Underwater Breathing Apparatus (SCUBA) device.
Fessenden oscillator
What is a device that counts footsteps called
smoke alarms, thickness gauges, neutron sources, gamma and beta rays sources, etc.
out put device