Medic James E. Callahan of Pittsfield, Mass., gives mouth-to-mouth resuscitation to a dying soldier in war zone D, about 50 miles northeast of Saigon, June 17, 1967. Thirty-one men of the 1st Infantry Division were reported killed in the guerrilla ambush, with more than 100 wounded. (Photo by Henri Huet/AP Photo)

A couple takes a selfie as Hoa Binh hydroelectric power plant opens the flood gates after a heavy rainfall caused by Talas typhoon in Hoa Binh province, outside Hanoi, Vietnam July 20, 2017. (Photo by Reuters/Kham)

A US Marine leads two Viet Cong suspects in restraints during the Tet Offensive on February 20, 1967. (Photo by Bettmann Archive/Getty Images)

A woman in costume of the Prosperity and Wealth God wears a protective face mask at a gold shop in Hanoi, Vietnam, Monday, February 3, 2020. It is a tradition for many Vietnamese to buy gold on the tenth day of the lunar new year – the day of Prosperity and Wealth God, for good luck. (Photo by Hau Dinh/AP Photo)

Vietnamese military personnel in traditional dress take part in a parade celebrating the 40th anniversary of the end of the Vietnam War which is also remembered as the fall of Saigon, in Ho Chi Minh City, Vietnam, Thursday, April 30, 2015. (Photo by Dita Alangkara/AP Photo)

Vietnamese female commissioned officers of the signal force march during a parade marking their 70th National Day at Ba Dinh square in Hanoi, Vietnam September 2, 2015. (Photo by Reuters/Kham)

Pham Thi Thanh drinks a glass of water used as a treatment during a medium ritual at a Hau Dong ceremony at Phu Day temple in Nam Dinh province, Vietnam, May 7, 2017. Dating to the 16th century, Hau Dong centres on a belief in the Mother Goddesses of three realms – forest, water and heaven. It draws from elements of Taoism, Buddhism and other religions. (Photo by Reuters/Kham)

People wear clothing to protect them from the heat while riding along a street in Hanoi, Vietnam, 24 April 2019. North and central Vietnam was recently affected by extreme hot weather, with the highest temperatures reaching over 40 degrees Celcius, according to the National Centre for Hydro-meteorological Forecasting. (Photo by Luong Thai Linh/EPA/EFE)