Speaking of sound and silence, is the photo below of the first Sonarmen in training?
Fessenden Submarine Oscillator (Source: NOAA)
In 1914 the Fessenden Oscillator was invented by Dr. Reginald Fessenden of the Submarine Signal Company in order to communicate between ships and between ships and shore facilities. The above photo is demonstrating a listening device, very similar to a telephone, used on board ships as part of Dr. Fessenden's system.
Additionally if your interested in doing some sonar watchstanding check out the following quick google of links:
NOAA Vents program Acoustic Monitoring.
Whale Acoustics research company's ocean sounds page.
J & A Enterprises, Inc. Noise and Vibration Control Engineers ocean sounds page.
And a large historical collection at the HNSA-Historic Naval Sound and Video webpage.
Finally a bit of computer geek trivia on the PING command, who knew it had anything to do with sonar.
Back in a week. -LL