This article talks about the submarine cable repairing. You may find this information at Wikipedia, but I took those information to summarize here for our readers.
Submarine cables can be broken by fishing trawlers, anchoring, undersea avalanches and even shark bites. Cable damages were common in the early cable laying era due to the use of simple materials and the laying of cables directly on the ocean floor rather than burying the cables in trenches in more vulnerable areas. Cables were also sometimes cut by enemy forces in wartime. Cable breaks are by no means a thing of the past, with more than 50 repairs a year in the Atlantic alone, and significant breaks in 2006 and 2008.
The damaged submarine cable portion is brought to the surface using a grapple in order to effect repair it. Deep sea cables must be cut at the seabed and each end separately brought to the surface, whereupon a new section is spliced in. The repaired cable is longer than the original, so the excess is deliberately laid in a ‘U’ shape on the seabed. A submersible can be used to repair cables that lie in shallower waters.
The damaged submarine cable is retrieved from the seafloor using a grapnel to snag and pull it up to the surface. After bringing it on board, the damaged sections will be removed. New cable sections will be spliced to reconnect the severed ends of the cable. The cable is then tested and brought back to the sea bottom.
A number of ports near important cable routes became homes to specialised cable repair ships. Halifax, Nova Scotia was home to a half dozen such vessels for most of the 20th century including long-lived vessels such as the CS Cyrus West Field, CS Minia and CS Mackay-Bennett.
The latter two were contracted to recover victims from the sinking of the RMS Titanic. The crews of these vessels developed many new techniques and devices to repair and improve cable laying, such as the “plough.
Typically, submarine cable repairing takes several days for the ship to reach fault position. Depending on the weather conditions, the repairing process will take 3-5 days once the ship is on site. Sometimes the repairing takes even longer if bad weather is involved.