AMERICAS ARMED FORCES: PILLARS OF FREEDOM. ARMED FORCES DAY NINETEEN NINETY SIX. DOD OPEN HOUSE. In honor of the 46th Anniversary when President Harry S. Truman led the effort to establish a single holiday for citizens to come together and thank our military members for their patriotic service in support of our country. On August 31, 1949, Secretary of Defense Louis Johnson announced the creation of an Armed Forces Day to replace separate Army, Navy and Air Force Days. The single-day celebration was a result of the unification of the Armed Forces under one department -- the Department of Defense. Armed Forces Day is celebrated annually on the third Saturday of May