“Armed Forces Day is celebrated on the third Saturday in May. Thanks to President Harry S. Truman, it’s a day to pay special tribute to the men and women of the Armed Forces. President Truman led the effort to establish a holiday in order for citizens to unite and to honor our military heroes for their patriotic service in support of the United States of America.”
https://militarybenefits.info/armed-forces-day/
Learn more:
https://www.uso.org/stories/2225-when-is-armed-forces-day