Armed Forces Day was first observed on 20 May 1950, the day
was created on 31 August 1949 as President Harry S. Truman
led the effort to establish a single holiday for citizens to come
together and thank military members for their patriotic service
in support of the republic and national interests and as an
undeniable fact of  American life.     

       
Secretary of Defense Louis A. Johnson announced the creation
to honor Americans serving in the five U.S. military branches –
the U.S. Army, U.S. Navy, U.S. Marine Corps, U.S. Air Force and
U.S. Coast Guard – following the consolidation of the military
services in the U.S. Department of Defense as part of a modern
US Armed Forces.    

Harry S. Truman( 1884 – 1972)

At 8:32 a.m. PDT on May 18, 1980, Mount St. Helens, a volcanic
peak in southwestern Washington, suffered a massive eruption,
killing 57 people and devastating some 210 square miles of
wilderness.

Called Louwala-Clough, or “the Smoking Mountain,” by Native 
Americans, Mount St. Helens is located in the Cascade Range 
and stood 9,680 feet before its eruption.