I like your thinking. Let me explain mine. From a purely logical point of view, maybe something like playing Sim City, Civilization, or other infratructure buil

I like your thinking. Let me explain mine. From a purely logical point of view, maybe something like playing Sim City, Civilization, or other infratructure building Sims this would make sense. In peace time, and if all players were like Spock, or of the same hive mind. Because like the BBC and Popular Science articles you linked this could be much more by co-bundling pipelines of all sorts (DATA!) with it, maybe even part of a global HVDC smart grid. The costs shouldn't really matter, compared to the money the military (No matter which) burns. It could also be the enabler of (environmentally responsible?) aquafarming, seasteading, nodes of wave- and offshore wind energy farming which would branch off from it. You'd need many platforms for security, emergency and maintenance reasons along the way anyways. But it would be very vulnerable and probably protested for all sorts of business and political reasons. Just look at what happens with proposed pipelines, high-speed rails, the bitching about where to put stations, the NIMBYism about where not, and so on. In this case there could be less NIMBYism, because open-seas, but think of the ship builders, and the giant complex of companies operating the built ships. Wouldn't you think they object to that? Just look at what ferry operators did when some tunnel or bridge opened, making them obsolete. So we have them, and their interests, against a potential network of submerged floating tunnels enabling all sorts of nice things, making them almost obsolete, too. Similar for Aerospace. 500kph seems doable without vacuum. Half the speed of air-traffic. 350 to 400 kph even more so, and already IS in operation at 350. Now imagine freight trains running at 250 to 300kph on separate tracks. Which you would want to have anyways, if only as reserve/backup for maintenance reasons. And now imagine a grid of these. Criss-crossing the seven seas, and having transport-hubs/nodes, switching yards, resort cities, free towns, permanent in-situ sensors, whatever, out there. Can't have pirates though, or war. What do you think about that? edit: I'd opt for smelting all the container giants, bulk carriers, and similarly obsolete stuff to build this. With nuclear power, if need be. I don't care. The same for most airplanes, because less noise. Seawards, Ho!