As a member of the North American Treaty Organization (NATO), Canada played an integral role in the defense of the West against the threat from the Soviet Union and its satellites in Eastern and Central Europe. Because of its relatively small population (currently about 34 million relative to the 300 million population of the United States) and its consequently much smaller military, Canadian contributions to the defense of the border separating West from East Germany were mainly symbolic and in keeping with its NATO treaty commitments. [Article V of the North Atlantic Treaty of 1949 stipulates that an attack on any member or members of the alliance shall be considered an attack on all treaty signatories.] Canadian military forces were stationed in Western Europe as a visible symbol of its commitment to its treaty obligations.
In addition to its role in the defense of Europe, and more substantial, has been Canada's integral role in the defense of North America. A product of its geography as well as its relationships with the United States and the North Atlantic Alliance, Canada played an important part in securing the northern reaches of the continent against Soviet military activities perceived as potentially threatening to it and to the United States. Canadian naval forces and aircraft routinely patroled the Arctic sea passages watching for and tracking Soviet submarines probing for weaknesses in those maritime transit routes.
The most visible Cold War Canadian role was in its partnership with the United States in defending the air space of North America through its participation in the North American Aerospace Defense Command (NORAD). Operating out of the Cheyenne Mountain complex in Colorado, NORAD monitors the skies above North America for signs of potentially hostile aircraft. During the Cold War, the Soviet Union frequently flew military aircraft along U.S. and Canadian borders to test NORAD's effectiveness as well as to practice for possible bombing attacks in the event of a war. Canadian fighter jets were routinely used to intercept such Soviet aircraft and escort those planes away from Canadian and U.S. airspace, a role also exercised on a regular basis by the United States, particularly in the air space around Alaska.
In addition, a network of radars are located along the U.S.-Canada border that are part of the U.S. ballistic missile defense warning system. Because the flight path of Soviet intercontinental ballistic missiles would have crossed over the Arctic region and over Canada, the Canadians were important contributors to the maintenance and monitoring of those radar systems.
Finally, Canadian intelligence services shared a very close relationship with other English-speaking U.S. allies, mainly Great Britain and Australia. Intelligence sharing among these countries' intelligence services was particularly close.