In general, the military connection to the interstate highway system is almost certainly overplayed. From what I've read, it's something Eisenhower wanted to do and the military aspect made it easier to sell to congress.
A major military aspect comes from a general logistics perspective. Eisenhower took part in a 1919 cross country motor convoy- it took 62 days to cross the United States, with many difficulties. That experience is regularly cited as a major influence on his desire to establish the interstate highways.
It’s not that they were built for the military, but the advantages to the military were also obvious.
That's fair enough. I have no doubt that, given his background, Eisenhower understood the value of a large country having a good way to move people and equipment around efficiently--whether for explicit military purposes or otherwise.
