High Quality Content by WIKIPEDIA articles! Puerto Ricans and people of Puerto Rican descent have participated as members of the United States Armed Forces in every conflict in which the United States has been involved since World War I. In World War II, Puerto Rican members of the U.S. armed forces guarded U.S. military installations in the Caribbean and took part in combat in the European and Pacific theatres.Puerto Ricans became U.S. citizens as a result of the 1917 Jones-Shafroth Act and were expected to serve in the military. When an Imperial Japanese Navy carrier fleet launched an unexpected attack on Pearl Harbor on December 7, 1941, Puerto Ricans were required to bear arms in defense of the United States. During World War II, more than 53,000 Puerto Ricans served in the U.S. Military.