I've always thought that we should have bought more Astutes (and less aircraft carriers)
There's also a clear need for more small patrol vessels to do the nitty gritty jobs that seem to fall to the Navy - and maybe stop having to use tankers & Argos as a fill-in
I can't see how you can protect pipelines tho' - the anwer is several methods of importing gas & oil - which we have to some extent.