Production and convoy questions

[WallysWorld]

I have really only two question so far about the demo:

1) Concerning the production or reinforcements that each side receives, does the player have any impact on the number and type of ships, planes or forces that each side receives? Or is it strictly based upon historical data?

2) What is the purpose of convoys? I understand the landing task groups are used to conquer bases, but what about convoy groups?

I'm having fun with the demo so I simply must write congratulations on the release. This game appears to be a winner.