Hi Greystone.
Whilst you will receive various radio reports of new bases being available.
You need to wait for your own radio message which will have your U-boat number.
Lorient becomes a base on July 1st 1940.
If you were docked in Wilhelmshaven you may have missed the message.
If you choose to dock in a French Port before you receive the above radio message you will get a reminder when you load the game that your home base has not yet changed and is still Wilhelmshaven.
Peter