The Royal Navy apparently considered an underground base for its missile subs to be located in the Loch Glendhu area in the North West Highlands. However, the US Navy wanted its submarines to be based closer to an airport and the Royal Navy wanted to be close to the US Navy...

I'm rather glad Loch Glendhu is left unspoiled but it does mean the current infrastructure for UK nuclear submarines is rather close to Glasgow and the largest population centre in Scotland.

Source: https://www.amazon.co.uk/Silent-Deep-Royal-Submarine-Service...

NB That book is worth it just for the description of the infamous Perisher course, let alone the stories about Rickover...