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Many of the world's internet backbone cables are underwater. But most of these cross deep oceans; how far could you bury cable up the Mississippi without anyone noticing? Could you reach St. Louis? Could you hide the existence of this backbone cable from the outside world, so long as it terminated in a relatively closed country somewhere in the Caribbean?

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    $\begingroup$ Possibly of interest: "The secret world of microwave networks" on Ars Technica; not really secret, but quite discrete and not generally known to the public. Separately, why would anybody want to keep secret the existence of the cable? Telecommunication companies will happily lease a fiber optics link from whatever city to whatever city, no questions asked (as long as the fee is paid on time, of course). $\endgroup$
    – AlexP
    Commented Mar 19, 2017 at 3:40
  • $\begingroup$ @AlexP Supposing the country it served had companies doing business at an uncompetitive rate, and a sort of cyberpunk business mentality... $\endgroup$
    – Adam Wykes
    Commented Mar 19, 2017 at 5:05

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Laying a fibre optic cable isn't terribly difficult, and even laying one underwater on the bed of the Mississippi river isn't outside of the bounds of possibility. What makes this difficult is your insistence that this be done covertly.

Since the Mississippi is one of the most heavily trafficked rivers in the world, with barge and riverboat traffic, a cable is not normally dropped on the river bed, but a channel is cut through the silt, the cable placed in the channel and then covered over for protection. Cable layers use a device which resembles a plow to carve the channel and cover over the cable. As well, keeping the cable anchored inside the channel eliminates mechanical stresses which might break the cable.

enter image description here

You need to tow that behind you the entire time

The other issue is that cables can only transmit light so far before the signal needs to be boosted. A handy calculator is here, but the general rule seems to be @ 2-3 km before the signal needs to be boosted. So there will need to be a parallel cable to provide electrical power to the amplifiers and regenerators. For obvious reasons, you don't want too many stations on the shoreline leading out to the cable.

Assuming you have the required equipment, putting the cable laying equipment on a barge or barge train and heading out into the river should not be too difficult. Disguising the shore station will be a bit tricky, and of course you will need to stop from time to time to splice lengths of cable together. As well, your barge will be going a bit slower than normal traffic due to the drag of pulling the plow, and the disturbed silt behind the barge might reveal that something is going on. The cable laying equipment could also be revealed either by accident or if the crew is careless or complacent. Getting the cable past flood control gates or locks on the river might also be an issue.

enter image description here

Barge train

Getting the cable laid from the mouth of the Mississippi river to the Caribbean simply transfers the problem from a barge to an oceangoing cable layer. There is also the possibility of crossing and cutting existing cables or other infrastructure which will reveal the cable when someone goes to fix the damage.

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    $\begingroup$ And if you do manage to overcome all those obstacles and get your cable laid, the next group to put a cable across the river will snag & cut yours, because it's not listed in the "Call before you dig" database. $\endgroup$
    – jamesqf
    Commented Mar 19, 2017 at 4:34
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    $\begingroup$ Ocean cables don’t have power added every few miles — it travels the length of the cable too. I've also seen writeups and photos of transoceanic cable stowed and payed out as one piece — not joined together en route. $\endgroup$
    – JDługosz
    Commented Mar 19, 2017 at 4:54
  • $\begingroup$ In the Mississippi, could you count on the river itself to bury the cable after a while? $\endgroup$
    – Adam Wykes
    Commented Mar 19, 2017 at 20:48
  • $\begingroup$ It is probably equally possible for the river to expose the cable as well. Better to go with the engineered solutions and bury it. $\endgroup$
    – Thucydides
    Commented Mar 20, 2017 at 2:55
  • $\begingroup$ I have seen the river change course several times in the duration of my life, but not once have I seen its riverbed exposed. Care to expand on that, @Thucydides $\endgroup$
    – Adam Wykes
    Commented Mar 21, 2017 at 3:17

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