There was an airport in Arlington before National Airport. It was born as Hoover Field in 1925 and evolved into Washington-Hoover Airport, named for then-Secretary of Commerce Herbert Hoover (and future president).
Here’s a great old photo of the airport terminal as it looked in 1942. It closed as an airport in 1941, the year that National Airport opened. The photo below shows it shortly before demolition began. The site is now where the Pentagon sits.