Though unsuccessful in carrying the cable across the ocean, this expedition was by no means a failure. Its results are thus summed up by the officers in charge of it:
- It was proved by the expedition of 1858 that a submarine telegraph cable could be laid between Ireland and Newfoundland, and messages transmitted through the same.
By the expedition of 1865 it has been fully demonstrated:
- That the insulation of a cable improves very much after its submersion in the cold deep water of the Atlantic, and that its conducting power is considerably increased thereby.
- That the steamship "Great Eastern," from her size and constant steadiness, and from the control over her afforded by the joint use of paddles and screw, renders it safe to lay an Atlantic cable in any weather.
- That in a depth of over two miles four attempts were made to grapple the cable. In three of them the cable was caught by the grapnel, and in the other the grapnel was fouled by the chain attached to it.
- That the paying-out machinery used on board the Great Eastern worked perfectly, and can be confidently relied on for laying cables across the Atlantic.