When the unit attacks the Japanese patrol with grenades, white phosphorus-type explosions are seen, but the soldiers seem to be carrying only standard Mk2 "pineapple" fragmentation grenades. Other explosions are seen but are too large for such grenades. A tropical zone grass would not burn so quickly, and the presence of dark black smoke indicates a petroleum accelerant was used for the scene.
(at around 10 mins) A 24-hour clock displays 01:00 hours (1 am). Then battleships are shown shelling an island, but the battleships are shown in broad daylight.
A pitched nighttime battle in the jungle is fought under a brilliant blue sky. Though the filter used to film the scene successfully darkened the set, the sky remained blue as opposed to black.
The tanks shown are M-26 Pershings, a tank that didn't come into use until the last months of the war and never was deployed in the island war of the Pacific theater.
The tanks are a variety of M4 Sherman, M-41 Walker Bulldog or M47 Patton and M-48 Patton tanks.
(at around 26 mins) As the sergeant is begging the lieutenant for more replacements, a mixed-race combat unit walks by in the background. The armed forces did not integrate until after WWII.
A recon team would never be landed behind enemy lines in broad daylight, and from a large, noisy landing craft. Then after they land there is a lot of talking in their normal voices and all the yelling with the snake bite scene, they cross open ground in daylight, and they smoke, which can also be a giveaway.
The recon mission is supposed to last four days, but the men are not carrying four days' worth of rations and especially not four days' worth of water for a tropical jungle environment.