I did operations for the P-3 for about 8 years in the Atlantic, Pacific, and especially the Middle East areas of responsibility.
I was Task Group Watch Officer qualified, and was trained to brief the aircrews on every little detail of their missions prior to departure. I have knowledge in all aspects of the P-3s capabilities.
OIIIIIIIO is right that hunting subs is not really a priority anymore, and that it has adopted more of a strictly surveillance/intelligence role.
Back in the 70s-80s, the P-3 was an extremely valuable asset because of its ability to hunt subs for long periods and over great distances. They also have the ability to kill, and they can carry torpedoes.
This was mostly because during the Cold War, the threat from subs was very great. Russia had a lot of them, and very advanced ones for the time.
Today though, the need to hunt, track, and kill subs is simply not a priority to the DOD. They are more concerned now with overland threats, and terrorism.
That’s not to say that the P-3 isn’t capable of this role, in fact it is. It’s just not something that it is used for a lot anymore.
Helicopters and ships are better at anti-submarine warfare by the way. The P-3 just brings great speed (in getting there), and long flight time into the equation, that’s what makes it a valuable ASW asset.