I'd like to bring up a point: the extra day to repair each point of damage is probably unrealistic, as the type of damage we're talking about couldn't be repaired by another submarine or a supply ship, but required a dedicated repair facility at a naval base. I don't know if it would be possible to make a distinction between supply vessels and port facilities, but I thought I'd mention it anyway.
Also, I apologize for not bringing it up back when the mods that allow milk-cows were in development, but I only just thought of it now.