With the escalating situation in Southeast Asia, in June 1964 28 B-52Fs were fitted with external racks for 24 750 pound (340 kg) bombs under project South Bay. An additional 46 aircraft received similar modifications under project Sun Bath. In March 1965, the United States commenced Operation Rolling Thunder, and the first combat mission of Operation Arc Light was flown by B-52Fs on 18 June 1965, when thirty bombers of the 9th and 441st Bombardment Squadrons struck a communist stronghold near Ben Cat in South Vietnam.