See my SIG.
I encountered (in sight) 2 taskforces in all my SH3 platime, one being a Battleship fleet (where I sunk a Revenge BB, see SIG) and another one, a small Carrier + escorts.
I knew the seccond one was a Carrier because I got atacked by swordfishes, and very soon after that Mr. DD and frends, ending my career rarther violently..
I don't do harbor raids because I feel that they are not protected enough as they where in real life, no air cover, loads of patroll ships and DD's etc. Atacking feels like an exploit to me.
Mid sea encounters are Very rare, another reason for me to keep playing SH3, I need at least one carrier kill before I even think of abandoning the game.
I suggest patrollign around the Gibraltar Strait, quite a few Taskforce reports there..