Only a comment to this mod. After playing U-boats
ad nauseam and getting our fill with US boats too, being able to play british submarines should be very high on the list. Compared with the US the british boats were much more similar to U-boats (i.e. smaller and lighter). Besides it would be a new perspective on things to see ports from the inside which we have been familiarized with being "hostile". For example, the landscape around Scapa Flow is very beautiful
And it would be interesting to start operations from the Lazaretto in Valetta, etc.