This dissertation examines the development of the North American air defence system from the beginning of the Cold War until 1956. It focuses on the political and diplomatic dynamics behind the emergence of these defences, which included several radar lines such as the Distant Early Warning (DEW) Line as well as a number of initiatives to enhance co-operation between the United States Air Force (USAF) and the Royal Canadian Air Force (RCAF). This thesis argues that these measures were shaped by two historical factors. The first was several different conceptions of what policy on air defence best served the Canadian national interest held by the Cabinet, the Department of External Affairs, the RCAF and the Other Government Departments (OGDs), namely Transport, Defence Production and Northern Affairs. For the Cabinet and External Affairs, their approach to air defence was motivated by the need to balance working with the Americans to defend the continent with the avoidance of any political fallout that would endanger the government‘s chance of reelection. Nationalist sentiments and the desire to ensure that Canada both benefited from these projects and that its sovereignty in the Arctic was protected further influenced these two groups. On the other hand, the RCAF was driven by a more functional approach to this issue, as they sought to work with the USAF to develop the best air defence system possible. Finally, the positions of the OGDs were shaped by more narrow priorities. For example, C.D. Howe and the Department of Defence Production sought to use these joint radar projects to build up the Canadian electronics industry. Canada‘s air defence policy in the 1950s, therefore, was a compromise between these various conceptions of the national interest. The other major influence on this process was the attitude of the Truman and Eisenhower administrations towards continental air defence. This dissertation will argue that most of the measures to improve the security of the continent emerged because of the efforts of the United States, but at the same time, the Americans‘ level of interest in these defences varied greatly over this period and ultimately were not sustained. Moreover, both these administrations had to overcome opposition from the USAF‘s senior leadership, which preferred an emphasis on the offensive nuclear forces of the Strategic Air Command (SAC) over improved air defences. This dissertation thus makes an important and original argument that contributes to the scholarly literature on the Canada-U.S. defence relationship during the early Cold War. / Thesis (Ph.D, History) -- Queen's University, 2011-09-14 14:08:14.101