Carrer: Change Base And Sub Type 1940

hi, it is july 1940, 7th flotille based in kiel and currently using a class VII. i have read (communitymanuals) about st nazaire being available in 1940 and about other available subs.

as a noob, what i would like to ask you is... when in 1940 does st nazaire become available (going around england is too long!)?? how?? i guess it will be seen in the transfers (telephone picture in the menu) but so far, nothing...

also i would like to ask you whether it's worth to change to a class ix. if yes, how should i do it? sorry for these noob questions, but since it is the carrer "branching" i thought i could ask.

thanks everyone.