Does a submerged sub disrupt a convoy?

You can’t pick and choose which enemy units in a space you attack.  If you attack one, you attack them all.  The only exception is when units of a power with which you are not at war also occupy the attacked sea zone.

@Krieghund:

There is no rolling versus defenseless transports.  By definition, transports that can retreat are not defenseless, so combat would be conducted normally.

Perfect. Thanks!

@Gravy:

Also, I’m attacking your lone sub with 2 of my own subs.  Do we all get a “first strike” ability since there are no destroyers involved.

Yes.

@Gravy:

I know you need a destroyer in order for planes to attack them but you don’t need a destroyer for lets say your battleship to attack an enemy sub do you?

No.

Commando Brado, wow this was a bad predicament to be in. I’m assuming that Japan was in allied hands and this was a last ditch effort to get it back (it gets one turn to do so). Boy did you get screwed by not having any ships that could take out those US subs, or force them to submerge. I didn’t think much of the a/c not having an attack value any more til now.

Edit: The only other scenario I could see where you would want to bring Jap transports into sz 6 combat is you still have Japan, and are trying to liberate Korea.

Yes, though such a movement would generally be made during noncombat movement.

@calvinhobbesliker:

If you move a sub into a SZ with 2 transports, are you allowed to just kill 1 and retreat the sub?

No.  They are both automatically destroyed.

@Hellmet:

Thanks all for the quick answers!!  Just a point of clarity, I assume that the sub must fight or flee on HIS (the US) combat turn and NOT Japan’s.

Of course.

right, so he can destroy the xport, or bombard, but not both.

If you destroy 12 IPCs as Japan the US is down to 38 or so. If Japan keeps up with the US Navy builds it seems like that would keep the Japanese on a pretty even playing field with the US.