Near the end of the movie, when Kuroda flips through the pages of the magazine, he repeats himself. In the close up he comes across the page filled with eyes, and then in the wider shot he again comes across that page.
Lee Marvin was 44 at the time of filming, as evident by his gray hair. Toshiro Mifune's character also calls him an "old man" several times. WWII US Navy pilots Thus, he looks much too old for an actual WWII US Navy pilot, who were mostly in their twenties or early thirties.
Fresh water is supposed to be precious on that island but you regularly hear birds in the background who must find it somewhere.