subdivision The GTR's bankruptcy in the early 1920s saw it nationalized by the Canadian federal government, which merged it into the nascent Canadian National Railways (CNR). Unfortunately for Portland, the CNR also included various other rail lines to ice-free Canadian ports in the Maritimes, notably Halifax, Nova Scotia, and their now ex-GTR mainline to Montreal soon became a secondary mainline under CNR as traffic dropped significantly. Within a decade, annual export tonnage leaving Portland declined to 21,000 tons, from an average of 600,000 tons during the early 1920s. Canadian National class S 2-8-2s pulled through freight trains between Portland and Island Pond, while class O USRA 0-6-0s worked those yards and class N-4 2-8-0s pulled local wayfreights within the United States. Passenger trains were usually pulled by locomotives working out of Montreal. Canadian National class E-7 2-6-0 #713 worked the Lewiston branch, and was preserved at the Canadian Railway Museum when 16 class GR-17 EMD GP9 diesel locomotives replaced steam power in 1957. Five of the GP9s were equipped with steam generators for passenger service, while the other eleven had dynamic brakes for freight service. Paper mills remained a major source of traffic. Annual car loadings in 1973 were 12,758 for Berlin, 5,794 for Groveton, and 1,161 for Mechanic Falls; but the Boston and Maine Railroad carried some of the traffic for the New Hampshire mills. Dressed meat from Chicago to Maine continued to use the shorter Canadian routing as long as railway reefers remained competitive with highway trucking. From 1934 to 1939 the twice-weekly Maine Coast Special from Montreal left the Grand Trunk at Yarmouth Junction to follow the Maine Central Railroad to Portland's Union Station and then the Boston and Maine Railroad to the beach communities of Old Orchard Beach and Kennebunkport during July and August. The CNR class U-1 4-8-2 locomotives pulling as many as 17 car trains around Dominion Day would be serviced at Rigby Yard in South Portland before making the return trip. Daily except Sunday passenger trains 16 and 17 continued to carry a railway post office between Portland and Island Pond through the 1950s. These trains remained popular with summer vacationers from Montreal, and summer weekend service continued until 1967 after daily train service ended in 1960. Passengers were transported by bus from Portland station to Old Orchard Beach. Portland station was razed in 1966. Despite the decline in traffic being handled over