James Christopher Monger of Allmusic selected the song as a top track pick, one of only two songs on the album to receive this honour and described the song as "brutal".
The song is about the terrifying experience being a soldier during Operation Overlord on D-Day of the 1944 World War II Battle of Normandy. The title of the song comes from the 1962 film The Longest Day which was based on the 1959 novel by Irish author Cornelius Ryan which was also titled The Longest Day. The song is considered a sequel by the band to the war epic Paschendale from the 2003 album Dance of Death written about the World War I battle of Passchendaele in 1917.
The song was played live during every show on the A Matter of Life and Death Tour as the band included the entire performance of the album during every setlist on the tour.