To locate a specific target or to determine how close submarines are to the seafloor, they use active and passive sound navigation and ranging (or a SONAR, in simple terms.) It emits pulses of sound waves that travel through the water, reflect off the target and relayed back to the ship. By determining how fast the sound wave travels back, the computers on the sub calculate how far they are from the target.
Hope this helps. 
        
                    
             
        
        
        
I'm not sure what you were trying to put here 
 
        
             
        
        
        
Speed of wave = Frequency x Wavelength
so Speed = 0.7 x 9 = 6.3
remember the calculations must be done in their Basic SI units.
therefore, you have to convert 7 mm to meters which becomes 0.7 meters
        
             
        
        
        
Answer:
 v= 449.8 m/s
Explanation:
Given data
Frequency=  346Hz
Wave length= 1.4m
The expression below is used to find the speed

substitute

Hence the speed is v= 449.8 m/s