Please don't put to much effort into the "undeclared war" to let US warships take part a few months early.
If you want to build something on the Arctic convoys King a good start would perhaps be making sure they are there at all to start with! Because currently, well they ain't....
When I fire up the Pearl Harbour Scenario as Soviet there are zero trades with USA running, the AI will not start up any if I run for 1 month and the US AI refuses to allow me dept or any trades.
As a matter of fact there arn't even any interesting trades since Soviet is running surplus on all basic resources and don't have enough money to buy any larger amounts off supplies. The only trade USA will even consider is buying my Soviet supplies, right about the opposite of what historically happened! Can you imagine Soviet tanks & ammo being exported to USA during the height of the battle of Moscow?!
(yes I know supplies is not equal to tanks but its probably the closest we will get in HoI3 since supplies = IC = Tanks).
But to put it bluntly the feature of the undeclared war wouldn't matter at all because there are no Arctic convoys running...
First you could start with making sure convoy routes are recalculated properly, at least once a month. The Arctic convoys would never run because the shortest route is Leningrad - Washington and that route is blocked when Germany takes over Denmark (the AI will cancel the trades/convoys though, but Soviet isn't always AI).
Secondly you could make sure USA gives Soviet alot off free supplies at least (through lend-lease events, decisions or otherwise). Without any supplies shipped there are nothing for any German submarines and ships to target and not even a reason for battle to begin with!
Thirdly you could make sure US can choose to use/donate its own convoys & escorts (since the game normally uses Soviet convoys when Soviet is the nation that is importing).
Another point that I feel is important about the battle of the Atlantic is that building convoys and escorts currently doesn't net any practical gains, so Soviet or Germany can build them just as efficiently as the USA can. This was NOT the historical case and a big reason for why USA had to help Soviet out defending the tradelanes and why Germany would have had such a hard time invading UK/USA (and would probably have failed even if they had tried).
Another nice thing about this is that it reflects the historical difficulties you describe when the UK fleet and merchant marine was stretched thin. In HoI3 SF UK can currently rebuild its entire starting merchantmarine and hundreds of Escorts in a single year if they focus on it, something that never was possible historically and that a bad practical value can assist in modelling (they can start a large construction program but it will take few years to net good result).
Thanks for the interview, always nice to hear about your plans and ideas at Paradox!
