A polar bear fast asleep at London Zoo. (Photo by Fox Photos/Getty Images). 1961

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 scavenger sifts through garbage piled on the bank of Beirut river, Lebanon August 24, 2015. Lebanese protest organisers called for a fresh demonstration against the government on Saturday after two days of rallies that turned violent in central Beirut and wounded scores of people. The “You Stink” campaign has mobilised against the government's failure to solve a garbage disposal crisis, bringing thousands of people onto the streets in protests that have threatened the survival of the cabinet. (Photo by Mohamed Azakir/Reuters)

A kid wearing rollerblades hitches a ride via motorbike, in Port-au-Prince, Haiti, Sunday, October 25, 2015. The country held the first-round presidential vote Sunday. Haitians chose between 54 presidential hopefuls and a slew of legislative and municipal candidates. (Photo by Ricardo Arduengo/AP Photo)

Williams Formula One driver Felipe Massa of Brazil crashes with his car in the first corner after the start of the German F1 Grand Prix at the Hockenheim racing circuit, July 20, 2014. (Photo by Kai Pfaffenbach/Reuters)

A tattoo of Captain America drawn by artist Sean Karon on the leg of client Ron Raucci at the Hampton Roads Tattoo Festival in Virginia, on March 2, 2012. The tattoo was completed from start to finish in one five-and-a-half hour session and won the prestigious “tattoo of the day” contest. (Photo by Jason Reed/Reuters)

Revelers celebrate during fireworks marking the start of the New Year on Copacabana beach on January 1, 2017 in Rio de Janeiro, Brazil. Brazilian revelers traditionally dress in white to honor the New Year's holiday along with the Brazilian Goddess of the Sea- Iemanja. (Photo by Mario Tama/Getty Images)

Caporal dancers perform during the carnival celebrations in Oruro, Bolivia, Saturday February 14, 2015. The Carnival of Oruro which is a religious festival dating back more than 2000 years in an ongoing pagan-catholic blend of religious practice in the region, and is one of UNESCO's Masterpieces of the Oral and Intangible Heritage of Humanity. (Photo by Juan Karita/AP Photo)