Review of Thirty Seconds Over Tokyo

When the movie starts, about 35 minutes in, the crew is landing in Florida for training info when I noticed a strange musical interlude. "Oklahoma where the wind comes sweeping down the plain..." No words, just the music, with just a few notes changed (to avoid copyright problems, I wonder?) but close enough to be unmistakable. Checking, I found this movie came out in 44 and Oklahoma had debuted on Broadway in 43. Coincidence? I wonder. It doesn't seem to have anything to do with the plot that I can tell, does it? I couldn't tell whether this had something to do with the movie or just a catchie piece of music the composer may or may not have realized he had heard somewhere before...