operations at the expense of civil airline development. C. D. Howe's role was critical in the founding of Trans-Canada Air Lines in 1937. Rather like the railways of the preceding century, TCA was founded as the national cross-continent carrier to keep out foreign competitors, and was made a subsidiary of CNR. See main article Air Canada#History. CPR was a part shareholder in Canadian Airways, and by 1941 CPR purchased Canadian Airways and other regional operations to form Canadian Pacific Air Lines in 1942. TCA, the government-controlled airline, was designated as the official transcontinental and international carrier by the Mackenize King government in 1943. For nearly forty years afterward, TCA and Air Canada benefitted from government regulation of air routes, fares, and standards of service. Government regulation was thought to be essential to prevent destructive competition between TCA and Canadian Airways. The two airlines, TCA and Canadian Airlines/CP Air, would remain bitter commercial and political rivals for the rest of the 20th century. Aerial photography Aerial photography was an urgent task for mapping remote regions of the country. War-surplus aircraft donated to Canada by the British and United States governments, or purchased by new private aviation companies, were the foundation of aerial survey and air photography in Canada. During the interwar period extensive air mapping was carried out by the RCAF. Mapping of remote regions from the air was valuable in developing forestry and mining resources in Canada's North. The operational experience gained during this time was a foundation of Commonwealth Air Training Program during World War II. International aviation Worldwide commercial civil aviation expanded greatly after the First World War. Many European countries founded subsidized national airlines (Sabena, KLM, Deutsche Luft Hansa, Air France and others) for reasons of national prestige, security and commerce. The United Kingdom founded Imperial Airways with the mandate of tying together the far-flung regions of the British Empire, providing air mail and passenger services for overseas British and allied territories. In the United States, the conditions of a large land mass, uniform language and culture, large and growing population, and good flying conditions, favoured rapid growth of private airlines. Many regional airlines grew, and looked to expand traffic to Canada and Latin America. In the United States, Pan American World Airways became unofficially virtually the national flag carrier, being given preferential support by the American government in its negotiations with other governments. Conditions in Canada