A submarine is a watercraft that can operate independently under the surface of the water. During a war, the naval submarines go under stealth mode of operation when the biggest threat is being detected. Anti-submarine warfare uses sonar equipment to track the submarines. During the stealth operation also known as silent running, efforts are made to minimize the noise produced by the submarine at all times. The speed of the craft is greatly reduced to minimize the propeller noise. Since being detected is the biggest threat, and water is a much better conductor of sound than air, all the unnecessary noise needs to be avoided, and that does include talking. But, is this sound enough to be detected? Here is the answer.
The speed of sound in water in much more than that in air. In order to know whether or not the noise from talking is enough to risk detection, we need to figure out the noise levels in the ocean. This risk also varies widely with the detection technique. This is what a passive sonar trace looks like:
The equipment generally relies on these sonar traces to hunt for submarines. The noise of a pan falling, or of a little scream is a transient that lasts for no longer than a few seconds. The noise levels in ocean waters are very high. One of the primary sources of this noise is merchant shipping. This ambient noise is even higher in shallower waters where there is more impact of wind and ships. Thus, the background noise in the waters is somewhat equivalent to a vacuum cleaner which is 70 dB. The noise from the most modern of nuclear submarines just one meter away from the hull is 110 dB. This is equivalent to the noise than you would hear standing on the taxiway as a jet takes off from the runway. If you are dropping pans, or even throwing stuff, this noise has to be louder than the noise the submarine itself is making. This should feel like dropping a tiny screw while the vacuum cleaner runs.
Keeping in view the passive sonar tracing and the noise the submarine itself makes, a little talking is no harm. In fact, talking is required for the operation and maintenance. As a general practice, however, all the crew that is not on the watch is instructed to be on their bunks and not make any noise. Even the food eaten at such times are sandwiches to keep the noise levels at a minimum. The reason is to instill in the crew the need for staying quite. If the sensors are close enough, even this little noise could be enough to be discovered.
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Credits: Ross Hall / Quora