Couple of Campaign Questions
 

1. How often do new submarines become available? And what are the requirements for being nominated as captain of a new sub? I've only been offered one new one so far...

2. Do most people stay based out of Pearl Harbor, or is it OK to transfer to another base of operations? Going from Pearl Harbor to Japan takes so long!

New boat types come along according to their historical dates of introduction. I'm not sure exactly how the game calculates when to offer you the upgrade, but I strongly suspect it has to do with your performance.

If by all means you want to transfer, go right ahead. Historically, transfers were common. The main difference you'll see is that your patrol areas will be different. Pearl based patrols usually get sent to the home islands for a large part of the war. I did get sent to the Marshalls and the Korean Strait a few times while based out of Pearl, so that's not a hard and fast rule.