@Stoney229:
can one make noncombat moves before declaring war, and then announce an attack on a convoy, thus declaring war after the noncombat move has been made?
Convoy attacks are not combat moves, or non combat moves. They are declared during the collect income phase of an opponent when you have ships in their convoy zone.
I believe that Japan could move their fleet into a seazone with a british convoy marker (and in fact a british fleet) while not at war. During the british turn, during their collect income phase, Japan decides whether they will interdict the convoy. At that point, a convoy attack is a declaration of war.