The UK and US have been using submarines as SIGINT platforms for a long time. Don't discount the ability to sneak into coastal waters a mile offshore from a missile testing facility, pop up an antenna and listen for telemetry, radar or other comms. The book I am currently reading about GCHQ describes such missions, for example: https://books.google.co.uk/books?id=l9i5bt1-7HYC&lpg=PA6&vq=...