Proposals for a road linking the contiguous United States to Alaska circulated from the 1920s, championed by Thomas MacDonald of the Bureau of Public Roads and dramatised by Slim Williams’s 1933 dog-sled journey along the proposed route. Canada under Mackenzie King repeatedly refused, fearing a US-funded highway across its territory would drag it into a Pacific war. Pearl Harbor changed everything: the Army approved construction in February 1942, Canada consented on condition the US paid every penny and handed over the Canadian section after the war, and the Army Corps of Engineers chose Route C to link the airfields of the Northwest Staging Route feeding Lend-Lease aircraft to the Soviet Union.

Over 10,000 men, roughly a third of them segregated African American troops of the 93rd, 95th and 97th regiments, punched a pioneer road from Dawson Creek to Delta Junction, meeting at Contact Creek on September 24, 1942. The episode covers the trail of discarded fuel drums that earned it the Oil Can Highway nickname, the disease that devastated the Indigenous village of Champagne, the permafrost that melted the road in 1943, corduroy log fixes, and the strange legacy of historic mileposts that no longer match a shrinking highway.

• Why Canada blocked the highway for two decades and what changed after December 7, 1941
• The debate over Routes A, B and C and the strategic logic of the Northwest Staging Route
• The irony that 99 percent of wartime supplies to Alaska still travelled by sea
• How stripping vegetation exposed permafrost and why modern engineers build up with gravel instead of digging down
• Historic Milepost 1422, the town of Wonowon and The Milepost guidebook published annually since 1949