Thanks a lot. There is a brilliant novel by William Deahl - "27". It's not exactly "alternative history", but more a plausible story about WWII intrigue and yes a German submarine at the US coasts is described there
Thanks dear! I intentionally made the submarine not so WWII type, they just do not look so interesting. Now need to make the UK flag to continue some WWII naval situations, it's easy but will need some layers, anyway we'll see.