Any land assault from a sea zone with neutral ships in same sea zone gets to defend against the attacking navy. Then you can attack Oslo from sea if trannys survive.
If you attack Oslo you want to attack from Finland and with German airborne [also fort doesnt get to defend] so when you capture Oslo the neutral ships are rolled for and become scuttle or UK or German ships.
See “how the carriers fight” in the manual. Carefully study that.
Although they don’t have an attack value and aren’t
represented on the battle strip, carriers can still participate
in an attack and can take hits, as long at least 1 unit with
an attack value attacks along with them. Any fighters or
tactical bombers on an aircraft carrier launch before the
carrier moves and move independently of the carrier.
These air units can make a combat move from the carrier’s
initial sea zone, or they can remain in that sea zone until
the Noncombat Move phase.
If your sub had hit the cruiser would have been sunk without firing back.
As the sub did not hit, the cruiser fires back.
If the cruiser does not hit either, the sub can continue the battle and has again a surprise strike (or retreats).
An enemy destroyer takes away the sub’s surprise strike ability.