There are times when a songwriter doesn't know what a song is about until after it is recorded. This song was a case of mistaken meaning. U2 frontman Bono says that when he wrote the lyrics, which detail a black car by the side of the road and a knock on the door, he thought he was writing about those who died in the conflict in Northern Ireland. After the song was released on the October album, he realized that the song was about his mother's death - she passed away when he was 14. What Bono was writing about was the morning of her funeral, and how he didn't want to get in the black car and be a part of it.
Vinnie Kilduff played the Uileann Pipes, a traditional Irish instrument. He's played with a number of Irish artists, including Clannad, Steve Wickham, and The Waterboys.
An early U2 song, "Tomorrow" is part of their second album, October, which like their first (Boy) was produced by Steve Lillywhite, who was also working with Peter Gabriel and XTC around this time. The song was part of the setlist for U2's 1983 War tour, but they never played it again after that trek.
In 1996, Bono and bass player Adam Clayton played on a version by the Irish folk singer Donal Lunny.