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. In 1932 Commonwealth & Dominion moved their head offices to Cunard House at 88 Leadenhall Street in London, sharing space with the Cunard Line. Also in 1932 Commonwealth & Dominion entered partnership with two other shipping companies, Ellerman & Bucknall and the New Zealand Shipping Company, to form the Montreal, Australia & New Zealand Line, to take over the Canadian National Steamship Line's services to Australasia. Commonwealth and Dominion officially re-branded itself 'Port Line Limited' on 18 November 1937. 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. In total thirteen ships were sunk, and another building programme was begun after the war. 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. With containerisation increasing, Port Line, Blue Star Line, Ellerman, Ben Line and the Charente Steamship Company formed Associated Container Transportation Ltd. on 12 January 1966, incorporating a subsidiary, Associated Container Transportation (Australia) Ltd., which would eventually supersede the Montreal, Australia & New Zealand Line. 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. The process continued with Cargo Equipment Service Co. Ltd. (CESCO) being formed in New Zealand to take over the equipment of Blueport, Shaw, Saville & Albion and the New Zealand Shipping Co., while in Australia the offices of Port Line and Blue Star were amalgamated with those of Ellerman & Bucknall to form Joint Cargo Services Ltd. New jointly operated shipping companies were created by the constituent companies to continue to operate shipping routes, including the Atlas Line and the Compass Line, which operated both Port Line and Blue Star Line ships. The Actanz Line was formed in 1969, consolidating all remaining conventional Port Line, Blue Star and Ellerman Lines ships under the title of Blue Star Port Lines (Management). Further management changes followed throughout the 1970s, with the fleets being steadily reduced in the face of containerization. Port Line withdrew from the now unprofitable Crusader Shipping in 1972, and in 1973 Joint Cargo Services Ltd was divided into two.