This is technical question regarding a theoretical situation. In the political rules Japan is excluded from moving to the United States’ coastline but Germany (or Italy) does not appear to have this restriction.
While Germany and the United States are not at war thus it would seem possible for Germany to move ships into the United States convoy lanes (without disruption, thus not declaring war) anytime during G1-G3. The United States, because of their political situation are thus unable to declare war on Germany and attack these ships.
On US3 it is obviously beneficial for the United States to declare war on the Axis at the end of their turn to start receiving their bonus IPCs. As this happens right before the collect income phase, they are at war with Germany and Germany is thus at war with the United States. The collect income phase happens and all prerequisites for convoy disruption are met and the US takes an immediate hit to their IPC gain. On G4 Germany can simply move this fleet away.
I am basing this on this post by Krieghund (topic=16001.msg539048#msg539048):
It all boils down to this: If you have a sub or surface warship in a convoy sea zone that’s adjacent to one or more of my territories during my Collect Income phase, you disrupt my convoy, unless you don’t want to.
Nothing else matters. It doesn’t matter what any of those ships did on your turn, my turn or anyone else’s turn. It doesn’t matter if I or anyone else has any ships of any type in the sea zone also.
I had read threads that said that convoy disruption had to be “declared” on the attacking player’s turn but the above-linked post seems to say it pretty much just boils down to the two requirements (ships in the convoy zone and being at war) as being met.
Is this a correct interpretation of these rules? Again, not asking for any strategy or counters on this particular tactic, just a ruling on whether or not it works as described.