The original harbour was built in 1736 for local trade purposes but is was never a satisfactory harbour.
The western arm of the breakwater was built between 1847 and 1864. By 1856 the western arm had reached 900yards (823m) and by 1864 the head of the breakwater had reached 1,600 yards (1463m). Wirj ib the eastern arm was never started. y the time that this had been built the size of warships had reached such as size that the new harbour was of little use due to the limited spcave, The arrival of the Ironclad, rendered the harbour built redunant,
A decision by the British Joint Naval and Military Committee on Defence decided that Alderney Harbour would be a suitable base for the torpedo-craft in time of war, assured. In 1891 the Harbour was designated a defended port, but this had been dropped early in the 20th Century.