Cairnryan is a small Scottish village overlooking Loch Ryan and is notable today for its large modern ferry port , operated by P&O , which links Scotland with Larne in Northern Ireland . Cairnryan is a small Scottish village overlooking Loch Ryan and is notable today for its large modern ferry port which opened in 1973 , originally operated by Townsend Thoresen and now by P&O Ferries , which links Scotland with Larne in Northern Ireland .