As per Wiki, the Ballad of the Green Berets" is a patriotic song in the ballad style about the Green Berets, an elite special force in the U.S. Army. It is one of the few popular songs of the Vietnam War years to cast the military in a positive light and in 1966 became a major hit, reaching No. 1 for five weeks on the Billboard Hot 100 and four weeks on Cashbox. Ultimately, the song was named Billboard's #1 single for the year 1966. It was also a crossover smash, reaching No. 1 on Billboard's Easy Listening chart and No. 2 on Billboard's Country survey.
The song was written by then Staff Sgt. Barry Sadler, beginning when he was training to be a Special Forces medic. The author Robin Moore, who wrote the book, The Green Berets, helped Sadler with the lyrics and get a recording contract with RCA Records.
The lyrics were written, in part, in honor of Green Beret U.S. Army Specialist 5 James Gabriel, Jr., the first native Hawaiian to die in Vietnam, who was killed by Viet Cong gunfire while on a training mission with the South Vietnamese Army on April 8, 1962. One verse mentioned Gabriel by name, but it was not used in the recorded version
Sadler recorded the song and eleven other tunes in New York in December 1965. The song and album, "Ballads of the Green Berets," were released in January 1966. He performed the song on television on January 30, 1966 on The Ed Sullivan Show, and on other TV shows including "Hollywood Palace" and "The Jimmy Dean Show." The song was the No. 1 hit in the U.S. for the five weeks, spanning March 1966 and the No. 1 hit on the Cashbox end of the year chart for 1966; also the No. 21 song of the 1960s as ranked by Joel Whitburn. The single sold more than nine million copies; the album, more than two million.