Actually, the UK did consider an underground base for its Polaris subs (probably around Lochalsh) but that got ruled out pretty quickly due to the enormous costs. The base also got relocated because the US wanted its UK submarine base to be close to an airport and the UK base ended up being close to the US base at Holy Loch.
Which is why the UK has its missile subs based so close to a major city!
See: The Silent Deep by James Jinks and Peter Hennessy
Which is why the UK has its missile subs based so close to a major city!
See: The Silent Deep by James Jinks and Peter Hennessy