Fear of a Japanese invasion during World War II is the reason this highway was built when it was. Built from 1942 to 1943, its original length was 1523 miles, but it is now 1,387 miles due to straightening and realigning over the years. The highway was officially opened on November 20, 1942 but wasn't completed until 1943. Completed in eight or nine months, depending on the source, it was a feat unequalled in modern roadbuilding, likely because 27,000 US Army engineers and civilians worked on the project.
Opened to the public in 1948 as a gravel road, the highway is now paved over its entire length. In peace time the highway has proved to be instrumental in opening the north to settlement and exploration.
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