[imported_Fluffy_Bunny]

There's a number of ways to find a sub, prop aircraft & helos can drop sonar bouys to find it & helos usually drop the dipping sonar which they can monitor as it sinks through the ocean. I guess it's handy for helos to use them as they can fit on the back of a frigate & be used where-ever the ship is rather than having to call on an aircraft carrier or land based aircaraft.

The Gizmos you saw on the prop aircraft were probably magnetic anomaly detectors (MAD). As subs travel through the earths magnetic field they create a magnetic anomaly because the submarine sturcture is made up of iron, this magnetic stuff is picked up by the MAD equiptment. The red, Russian, commie, bastrds countered this by making a sub out of titanium cuss: Interesting stuff...