>Yep, because now you've just got your air rushing into the vacuum through the cracks, instead of water.
Fair enough. I imagine there's a trade-off between the quality of the tunnel materials and the number of pumps needed along the way, assuming an imperfect vacuum is good enough.
I'd be worried about flexibility too. Skyscrapers do pretty well in high winds and earthquakes, so I'm not completely convinced that a similar effect isn't possible with an underwater tube. Any bending would have to be extremely gradual, though, if there's any hope of shooting something through it at high speeds. I agree that glass isn't going to cut it.
Fair enough. I imagine there's a trade-off between the quality of the tunnel materials and the number of pumps needed along the way, assuming an imperfect vacuum is good enough.
I'd be worried about flexibility too. Skyscrapers do pretty well in high winds and earthquakes, so I'm not completely convinced that a similar effect isn't possible with an underwater tube. Any bending would have to be extremely gradual, though, if there's any hope of shooting something through it at high speeds. I agree that glass isn't going to cut it.