After the Japanese attack on Pearl Harbor, a fear of invasion swept North America—particularly the West Coast. Immediate steps needed to be taken to defend the Far Northwest. With Canada’s approval, Washington drew up plans for an Alaska Highway to connect Edmonton, Alberta, with Fairbanks, Alaska, and a pipeline to connect oil fields in the Northwest Territories with the Pacific Coast. Between 1942 and 1946, about 40,000 American military and civilian personnel invaded the Canadian Northwest. Where there had been few or no roads, a highway more than 1,500 miles long was built in less than a year. Navigation facilities were improved, and pipelines were laid from Fairbanks to the Pacific. Airfields were upgraded and new ones built, and a telephone network was constructed. The Northwest was totally unprepared for this friendly invasion. The Alaska Highway ran through semi-wilderness where many inhabitants pursued a nomadic lifestyle, and towns and settlements were overwhelmed by the American “army of occupation.” This lively history of an American civil and military engineering milestone draws on interviews with veterans and local residents and research in Canadian and U.S. archives. The participants’ stories provide humor and insights on the building of this transformational highway.