Every now and then, you'll hear reports of undersea cables getting hit by a ship's anchor, destroying landline connectivity between continents. More than often, you'll also hear the "terrorist" term being mentioned. Not unreasonable, seeing as how vulnerable our Internet's Backbone really is. The following image shows the layout of nearly all undersea cables.
Very fragible ... There was a very interesting video round-up by Discovery Channel, on how those cables are being deployed (in this case, for Global Crossing). It _was_ worth a watch, before they deleted it -_-.