The Blogger’s Best Friend ™ tells us that Bobby wrote this song whie he was serving in the Army and recorded it on his 1962 album Roses Are Red. It wasn’t released as a single until 1964, just as the US was ramping up its involvement in Vietnam. That probably was part of the reason it did so well: it spent 15 weeks on the Hot 100, reaching #1 a couple of weeks before Christmas 1964. It was also a #1 in Canada, #2 in New Zealand, #8 in Australia, and #3 in South Africa.
Interesting story about this: Bobby wanted to release it as a single in 1962, but Epic Records gave the song to Buddy Greco, whose version reached #64. When confronted, Epic’s management said they did that because they didn’t think of Bobby as a singer, but as a musician and songwriter. It turns out that Bobby was Epic’s most successful artist in the ’60’s.