Biên Hòa is a city in Đồng Nai Province, Vietnam, about 30 kilometres (20 mi) east of Hồ Chí Minh City. Following the First Indochina War (1946-1954), tens of thousands of refugees from the northern and central regions of Vietnam—a large portion of whom were Roman Catholics — resettled in Biên Hòa as part of Operation Passage to Freedom. During the Second Indochina War (1955-1975), the United States Air Force operated Biên Hòa Air Base near the city. Mortar attacks on US and Army of the Republic of Vietnam (ARVN) targets were frequently staged from residential districts in Biên Hòa. Two of the better-known attacks took place during Tet of 1968 as well as 1969.