In the spring of 1965, within weeks of 3,500 American Marines arriving in Vietnam, a 39-year-old Briton named Larry Burrows began work on a feature for LIFE magazine, chronicling the day-to-day experience of U.S. troops on the ground – and in the air – in the midst of the rapidly widening war. The photographs in this gallery focus on a calamitous March 31, 1965, helicopter mission; Burrows’ “report from Da Nang”, featuring his pictures and his personal account of the harrowing operation, was published two weeks later as a now-famous cover story in the April 16, 1965, issue of LIFE.

Photo: Man your battle stations: The crew chief of helicopter Yankee Papa 13, lance corporal James C. Farley, mans an M-60 machine gun during a mission near Da Nang, Vietnam on March 31, 1965. (Photo by Larry Burrows/Time & Life Pictures)

In this photograph taken on April 16, 2014, a veterinary staff member of the Sumatran Orangutan Conservation Programme center conducts medical examinations on a 14-year-old male orangutan found with air gun metal pellets embedded in his body in Sibolangit district in northern Sumatra island. (Photo by Sutanta Aditya/AFP Photo)

Goats jumps to cross a stream as they are driven by a herdsman at Dashiwo village, on the outskirts of Beijing January 26, 2015. The Chinese Lunar New Year on February 19 will welcome the Year of the Sheep (also known as the Year of the Goat or Ram). (Photo by Kim Kyung-Hoon/Reuters)

Hundreds of green bicycles are prepared as 960 of them await riders for the new year gala at the Temple of Heaven Park on December 29, 2011 in Beijing, China. Annual New Year countdown ceremony will be held at the park on December 31. (Photo by ChinaFotoPress/ChinaFotoPress via Getty Images)

An employee works on a glass sphere for Christmas and New Year decoration at the “Biryusinka” toy factory, which has been producing decorations and toys for the festive season since 1942, in the Siberian city of Krasnoyarsk, Russia, November 16, 2016. (Photo by Ilya Naymushin/Reuters)

People watch dragon dance performance in front of a business establishment in celebration of Chinese New Year at Manila's Chinatown district of Binondo, Philippines, Friday, January 31, 2014. (Photo by Bullit Marquez/AP Photo)

A woman surveys the damage after the earthquake on March 17, 2011 in Kensennuma, Japan. Residents were allowed back to their homes today and began the massive cleanup operation caused by a 9.0 magnitude strong earthquake that struck on March 11 off the coast of north-eastern Japan. The quake triggered a tsunami wave of up to 10 metres which engulfed large parts of north-eastern Japan. The death toll has risen past 5000 with at least 8600 people still missing. (Photo by Chris McGrath/Getty Images)