No. Scrambling occurs during the Conduct Combat phase, so all combat movements will have been completed. Scrambling only occurs in sea zones in which attacking units end their combat movement.
While the US is not at war, it may not use UK or ANZAC naval bases, and UK/ANZAC may not use US bases. UK and ANZAC are always free to use each other’s bases.
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.