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.
This is true more generally. When I lived in London and the IRA campaign was going on I never understood why they didn't just set fire to a few stolen vans on Euston road/City road/Waterloo bridge every morning rather than actually killing people. Would have been more effective.
At the time, London transport was pretty much at gridlock anyway and made the city pretty hard to live in IMO. It wouldn't have taken much to threaten the major income-generating source of the country (look up the economics of the city of London).
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).
How so? I lived in the city and this is what I thought at the time. I might have been mistaken (which is part why I posted it here... to hear alternative arguments).
