Gun enthusiasts look over Smith & Wesson pistols at the NRA Annual Meetings & Exhibits on May 21, 2016 in Louisville, Kentucky. About 80,000 visitors are expected to attend the three-day event. (Photo by Scott Olson/Getty Images)

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)

A weapon is being destroyed during an exercise to disable seized weapons in Caracas, Venezuela August 17, 2016. (Photo by Marco Bello/Reuters)

Convicted murderer Hector Alvarado Mazariegos, right, drops to the ground as he is hit by bullets of a Guatemala firing squad in the public cemetery at Mazatenango, June 28, 1975. His companion, Rocael Ortiz, met the same fate a few seconds later. Both were convicted of murder. (Photo by AP Photo/Anzueto)

A man looks at a photograph by French photographer Robert Doisneau entitled “The Fate Line: Pablo Picasso at Vallauris, 1952” during the presentation of the photo-exhibition “Picasso, photographer's gaze”, on June 5, 2019 at the Picasso Museum in Barcelona. (Photo by Lluis Gene/AFP Photo)

Castro's soldiers at Playa de Giron, Cuba, after thwarting the ill-fated US backed 'Bay of Pigs' invasion. (Photo by Graf/Getty Images). April, 1961