I think HMS Courageous is closed to the public at the moment. No explanation was given, but it might be because at least one T boat is being decommissioned at Devonport at the moment.

I know nothing of the Cold War Centre - it wasn't mentioned at the time. I think the best thing to do is to ask the question on their FB page - same for opening hours. If you are ever planning to attend please let me know. I live in Plymouth and would be pleased to meet up for a coffee and exchange of views etc.