 To take pressure off the harbour facilities the British Admiralty, decided to lay in heavy moorings off the harbour for its battleships, and to facilitate that, they imported from Britain an air lock diving-bell plant, a purpose-built barge in 1902.Local conditions at Gibraltar dictated the need for such a craft.Most harbours have a soft seabed, and it is usual to lay down moorings by settling anchors in the mud, clay or sand but this could not be done in Gibraltar harbour, where the seabed is hard rock, requiring permanent moorings in place.