The Longest Day was an all-star portrayal of D-Day. And by "all-star" I mean "perhaps the most all-star cast ever" for a film. It was so all-star that Richard Burton and Roddy McDowell who weren't cast begged to do a cameo - and flew themselves to Normandy on their own dime and did the cameos for no salary. The actors thought that the upcoming 20th anniversary of the invasion was important enough that the big name actors only took $25,000 each to keep costs down - except for John Wayne who was mad at the director and insisted on his usual fee of $250,000.
"All-star" extended beyond the on-screen talent. Screenwriting credits included Noel Coward and Erich Maria Remarque (author of "All Quiet On The Western Front"). And the musical score was composed by Maurice Jarre who was to get two Oscar nominations that year - one of which took home the prize: Lawrence of Arabia, which we've seen here before.
The score sounds a bit dated, because audience expectations have changed over the years. Now the focus is on those who didn't come back, best exemplified by John Williams' Hymn For The Fallen. Back in 1962 the focus was on the victory, and so the music was much more, well, martial. But who's to say that they were wrong? The Second World War was so big that focusing on the win, rather than the enormous number of losses seems a plausible approach to handling the emotions. And it was this Republic's last war victory; seventy years of losses or draws can change a public's outlook.
Me, I'm willing to defer to the judgement of those who were there at the time. It was their tribute to those present at that Day of Days.