"... the existence of the PR industry, lurking like a huge, quiet submarine beneath the news".

I agree, this interpretation seems more likely than submarine patent [0]: "Analogous to a submarine, therefore, submarine patents could stay "under water" for long periods until they "emerged" and surprised the relevant market. Persons or companies making use of submarine patents are sometimes referred to as patent pirates"

[0] https://en.wikipedia.org/wiki/Submarine_patent