US turn 2
Japan isn’t at war with anyone, except China.
Japan has a transport in SZ 6, with no warships
The US moves their sub into this sea zone

Japan turn 3, they declare war
Does the US sub get to shoot immediately?
Does it get to shoot, if Japan attempts to move the transport?
Can Japan move a surface warship into the sea zone, stop the attack, then load and move the transport?