Armed Forces Day is a special holiday for people all over the world, and to thank the men and women of the United States Armed Forces. First time President Harry S. The holiday was founded in 1949 by Truman. Due to recent consolidation under the Department of Defense, a single day celebration was created for all five branches of the United States Army. Today, Armed Forces Day is celebrated on the third Saturday of every year, and falls on May 16 this year. Mark your calendar and support our military.