[Snakeeyes]

Okay... I've read lots of good fiction on modern SSNs... I love it.

I think that I am rapidly going down in this forum as "The Annoying Questioner" but you guys are such great sources of wisdom! (sucking up supreme).

What is the difference between a transient noise and a tonal noise?

I always assumed that transient noises are the sounds coming from machinery running on board a boat... the generators... the cooling pumps... etc.

Is this right?

My only guess for "tonal contacts" are those which can be heard with the headphones on.

[Bill Nichols]

A transient is a noise that is only heard for a short time, such as from opening a torpedo tube door or launching a weapon.

A tonal is a sound that can be detected at discrete frequencies. For example, a 60-cycle 'hum' from a transformer can be considered a tonal. Submarine tonals are most commonly generated by rotating machinery (pumps, motors, generators, reduction gear, etc.) and are usually persistent (i.e., always there).

[Fitz62STG]

Also transients even though short duration, can be extremely loud. Hence allowing you to gain a contact at a farther range. Due to their short duration nature though requires that you pay extra attention to your displays so you can detect them and keep track of them while you are driving in to gain narrowband contact.

Transients can be - burst of cavitation, weapon launch (doors opening etc..), hull pops, pretty much anything that makes a detectable noise that is not around for very long.