Conversation so far:
what is a common local holiday in the philippines
The Day of Valor on April 9th is a common holiday in the Philippines.
What does Day of Valor commemorate
Day of Valor or Bataan Day is a national observance in the Philippines which commemorates the fall of Bataan during World War II.
Who fought in the Battle of Bataan
The Battle of Bataan was a battle fought by the United States and the Philippine Commonwealth against Japan during World War II
When did the Battle of Bataan take place
The Battle of Bataan was fought from January 7 to April 9, 1942.

Question: When did the holiday start being observed
Self-contained rewrite: When did the Day of Valor start being observed