Every subsea cable service interruption story is an excuse to share one of my favorite pieces of long-form technical history: Neal Stephenson's Mother Earth Mother Board:
The Wired article is paywalled now unfortunately. Here's an archived version:
https://web.archive.org/web/20210107003422/https://www.wired...
The Verge also has a great article which is more recent and more specifically about a repair ship:
https://web.archive.org/web/20240422050805/https://www.theve...
Multiple subsea fiber cuts in the Red Sea impacting global communications
Impact Summary
Starting at 05:45 UTC on 06 September 2025, traffic traversing through the Middle East originating and/or terminating in Asia or Europe regions may experience increased latency due to multiple undersea fiber cuts in the Red Sea. The disruption has required rerouting through alternate paths which may lead to higher-than-normal latencies.
This advisory is intended to raise awareness ahead of increased demand as the regions enter the start of its work week.
Current Status
Multiple international subsea cables were cut in the Red Sea. Our engineering teams are actively managing the interruption via diverse capacity and traffic rerouting, while also discussing alternate capacity options and providers in the region.
Undersea fiber cuts can take time to repair, as such we will continuously monitor, rebalance, and optimize routing to reduce customer impact in the meantime. We’ll continue to provide daily updates, or sooner if conditions change.
This message was last updated at 19:30 UTC on 06 September 2025
The smart folks who keep these things running, despite failures like this, are incredible. Hats off to you all, good luck in the coming weeks as you have to deal with this.
https://www.bbc.com/future/article/20241014-the-deep-sea-eme...
An article about people who fix this
Also, the teams are quite busy:
> "There are 150 to 200 instances of damage to the global network each year. So if we look at that against 1.4 million km, that's not very many, and for the most part, when this damage happens, it can be repaired relatively quickly."
...
> If a fault is found, a repair ship is dispatched. "All these vessels are strategically placed around the world to be 10-12 days from base to port,"
...
> To repair the damage, the ship deploys a grapnel, or grappling hook, to lift and snip the cable, pulling one loose end up to the surface and reeling it in across the bow with large, motorised drums. The damaged section is then winched into an internal room and analysed for a fault, repaired, tested by sending a signal back to land from the boat, sealed and then attached to a buoy while the process is repeated on the other end of the cable.
I wonder how much slack is left in the cable over its run in order to facilitate bringing it up for repair.
At first it’s an average of 1% slack across the entire run but up to 5% in rough terrain. They don’t use slack though for repairs, they lay down new cable between the bights that adds up to several miles to the length.
Now that’s what i call a service loop!
> 1.4 million km
Strange way of writing 1.4gm.
Do you also write gigagrams?
Usually I write "pounds," but what I usually write isn't the point.
Should be 1.4Gm
Gram-metres?
Hahaha.
Hosted by my own petard. :)
BGP <3
Yes, but it's damn time people start upgrading to BGP ==3.
Most likely not. Almost certainly bfd or ldp/mpls
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An act of terrorism is never smart or heroic.
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Free the hostages then we can talk
Yeah all of the Palestinians that Israel has been holding hostage since well before Oct 7th need to be freed.
Were they cut on purpose or accident?
Cables in Red Sea got cut frequently. All the time it's the same story - anchor dropped where it should not. Similar stories happen near Singapore.
> Cables in Red Sea got cut frequently
On land, we’ve call before you dig. I wish they could do something like call before you drop (anchor) training or just get the word out.
They are usually marked on nautical charts.
Some fishermen won't care as there are less ships where the cables are, they'll fish there. There are a lot of cables and fishing vessels in the Irish Sea.
Couldn't that be a security concern?
Security concern is the more unlikely scenario of accidental cutting. There is enough redundancy that it is very difficult to cut them all for a single ship and if there are hypothetically multiple ships all cutting at the same time, then it is likely to be traceable. The cost of cutting these cables by sending someone out there is significant enough in addition to how unlikely they are to succeed.
(It’s not actually anchors.)
It very often _is_ an anchor, and they are usually dropped and dragged on purpose for the effect of cutting the cables which are clearly marked on charts as places to not drop anchor
The chances of it being due to accident seems astronomically low, but I didn’t realize the intentional cutting was by an actual anchor. That makes sense though, as it would be an easy, discreet method.
Why do you say that?
I can't say I'm an expert on the matter, but my understanding from industry reporting on some likely intentional ones in the Baltic where that they were still unambiguously done with anchors. Just by someone intentionally causing the anchor to drop and drag along.
Cable cuts are very common worldwide and are very rarely reported widely in the media ( that I've seen ) unless there's an opportunity to tie it to Russia. Then it's reported as suspicious or there's a paragraph in the article speculating about the security implications of purposeful attacks on communications infrastructure. IMO it's a ploy to generate anxiety about how much money is being spent on "security" i.e. the military, and how we ( Europe ) need to increase it.
Found the propagandist.
It's by far the most common.. but.. Multiple cables in this manner is IME /less/ likely to be an anchor, although it has happened.
I meant they are intentional, as opposed to being a side-effect of ‘anchoring’ the boat to keep it from moving.
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You mean no Russian or Chinese ships deliberating cutting cables on land like in EU ? That can't be /s
A captain told me once that it is silly to assume a big ship dropps it’s anchor accidentally unnoted
You need to run a whole procedure to get the anchor dropped. It can't be an "accident" in any means.
And red sea is quite sunny currently (i just checked windy.com now) . There is absolutely no reason that they need to drop it out of nowhere.
But it’s a somewhat believable cover story when you’re running military sabotage ops from a civilian vessel
It's only been a few hours. I doubt anyone knows.
Can they splice these? Surely the don't have to run a whole new cable?
They can but it's an involved process. Modern cables manage their slack very precisely - a complicated job in and of itself - and usually cannot be hauled to the surface without snapping them. So if the cable is not already cut (an anchor can damage a cable in a variety of ways short of physically snapping it) it will be cut while still on the bottom. The ends are then winched up and a splice is patched in but now there's a rather lengthy section of extra cable to deal with. They deal with that by laying it down precisely on the seabed in a nice sideways loop.
So then you have extra latency for each repair.
And extra attenuation / reflections.
I've only done land based fiber design, but I would assume based on my experience in that field that one of two things happens.
First option, there's some slack somewhere nearby to do a pull nearby.
If you ever pay attention to aerial poles, you'll see at various intervals things that are vaguely reminiscent of a snowshoe or tennis racket, in the industry they are in fact informally referred to as a 'snowshoe' and the entire purpose is to have some fiber to 'release' if a cut happens and a resplice is needed. [0]
I'd -assume- there is an analogue for these in undersea cables...
If not, well then you'd have to splice a length in and probably have the right sort of mechanism to ensure the cladding/etc stays contiguous (maybe even weld? IDK) but regardless you're probably talking... Actually wait yeah they've got this all figured out; https://www.youtube.com/watch?v=QiwidMEv8CM
[0] - Real world example, for instance if someone uses a fiber splice can for target practice.
https://www.bbc.com/future/article/20241014-the-deep-sea-eme...
An article about such repairs (150-200 yearly)
> To repair the damage, the ship deploys a grapnel, or grappling hook, to lift and snip the cable, pulling one loose end up to the surface and reeling it in across the bow with large, motorised drums. The damaged section is then winched into an internal room and analysed for a fault, repaired, tested by sending a signal back to land from the boat, sealed and then attached to a buoy while the process is repeated on the other end of the cable.
I think they raise the cable to the surface, splice it and sink it again.
I've read (or perhaps watched on YouTube) the same thing.
Finding both ends of the cable to grab abd raise it took longer than the raise/splice operation.
I suspect a sufficiently malicious attacker could intentionally cut the cable twice, so when the repair crew drag up one end of the cut they know about, the section between the cuts drags its other end away from it's cut-point making the second repair significantly more difficult...
In most cases they can easily figure out approximately where the break is on the line by simply measuring the resistance in the cable's conductors (they have more than one but the big one caries a 10,000V feed to power the repeaters). A double cut would probably show up as resistances that didn't sum to the proper total.
You can only practically do that optically e.g through OTDR. You can't TDR steel conductors exposed to the ocean 500KM away with a ohm meter and a Murray loop, to even have a chance you need to put low voltage on it and it's not even close to as accurate.
Rubbish. TDR is not a Murray loop.
https://en.m.wikipedia.org/wiki/Murray_loop_bridge
Spread-spectrum time-domain reflectometry (SS-TDR) is often used to locate and characterize a fault on active cables. Traditional time-domain reflectometry, which sends signals down a conductor to determine where any impedance discontinuities are by timing any reflections that come back from any impedance discontinuities along the way, can’t be used on in-use undersea cables thanks to the high voltages involved. SS-TDR, which was originally developed to detect faults in the wiring of airplanes using 400-Hz AC power, uses modulated pseudo-noise (PN) signals rather than a plain square wave pulse. The signals still bounce off any impedance changes introduced by damage, but an algorithm is used to correlate the returned PN codes with what was sent and when, making it easier to make measurements in a noisy environment. Optical TDR can also be used to locate fiber breaks
A little knowledge goes a long way
Cutting twice wouldn't be an issue, they can send a signal from both ends to get a reflection of how much of the cable is dead.
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