It does legitimately seem like you can do tremendous damage by derailing a few ships in the right spots. Bringing bombs or other small ships or something else seems doable for a terrorist organization on the face of it.
And what government would cave to whats essentially a minor inconvenience
I don't even think it requires you to throw your life away. It could just be classified as civil disobedience.
To be clear, I had no sympathy at all with the IRAs violent campaign. I'm just pointing out that committed civil disobedience could be pretty effective if you have people committed enough that they will already kill people and go to prison quite often (or blow themselves up for that matter).