Reflecting the make up of its constituting companies, the ships of the new line adopted a varied arrangement of existing styles.

The ships flew Tyser's house flag but had Corry's funnel colours of buff with black tops.

The company remained profitable during the Great Depression, and between 1927 and 1932 shipped steel girders from Middlesbrough for use in the construction of the Sydney Harbour Bridge.

The company suffered a number of losses during the Second World War to a variety of causes, including accidents, submarines, surface raiders and air attacks.

Port Line entered another partnership in 1957, combining with the Blue Star Line, Shaw, Savill & Albion and the New Zealand Shipping Company, to form the Crusader Shipping Co. Ltd., to trade between New Zealand, the Far East and the Pacific coast of North America.

However a process of retrenchment at Cunard in 1968 saw the incorporation of Blue Star Port Line (Management) Ltd, also known as 'Blueport', to cut costs.

Port Line withdrew from the now unprofitable Crusader Shipping in 1972, and in 1973 Joint Cargo Services Ltd was divided into two.

The last remaining conventional cargo ships still owned by the group at this point were transferred to Cunard-Brocklebank's control, ending Port Line's existence as an autonomous business entity.