The Navy League of the United States organized the first Navy Day in 1922, holding it on October 27th because it was the birthday of President Theodore Roosevelt, who was a naval enthusiast. In 1923 over 50 major cities participated, and the U. S. Navy sent a number of its ships to various port cities for the occasion. The 1945 Navy Day was an especially large celebration, with President Harry S. Truman reviewing the fleet in New York Harbor.
In1949, Louis A Johnson, secretary of the newly created Department of Defense, directed that the U. S. Navy participation occur on Armed Forces day in May, although as a civilian organization the Navy League was not affected by his directive. They continued to organize Navy Day celebrations to suit themselves until it was discovered in the 1970s that the “birthday” of the Continental Navy was actually October 13, 1775. Admiral Zumwalt worked with the Navy League to define October 13th as the new date of Navy Day, though some still celebrate it later as originally organized. (me and Wikipedia)