CS Dependable at Astoria, Oregon, a modern stern sheave design.
A cable layer or cable ship is a deep-sea vessel designed and used to lay underwater cables for telecommunications, electric power transmission, or other purposes. Cable ships are distinguished by large cable sheaves1 for guiding cable over bow or stern or both. Bow sheaves,2 some very large, were characteristic of all cable ships. Newer ships are tending toward pure stern layers with stern sheaves only as seen in the photo of CS Cable Innovator at the Port of Astoria on this page. The names of cable ships are often preceded by "C.S." as in CS Long Lines.3
The first transatlantic telegraph cable was laid by cable layers from 1857–58. It briefly enabled telecommunication between Europe and North America before misuse resulted in failure of the line. In 1866 the SS Great Eastern successfully laid two transatlantic cables, securing future communication between the continents.