At 29:40 the "Destroyer" (a battleship) is shown in moderate seas (with waves), when the shark is attacking, the sea has calmed, and the ship is shown without a wake at the bow.
In each subsequent closeup of the ship - waves, from farther out - no waves, no wake.
At 44:55 the radar operator states the Black Bird is descending to elevation 6-5-0 (650 ft.)
At 45:12 Fernando (Allan?) says the plane is "about a hundred feet off the deck."
In this universe, on this planet, "the deck" is the surface of the ocean and is what all elevations are calibrated to. (mean height of ocean)
When the shark and octopus attack each other for the first time, the shark bites off one of the the octopus' tentacles to break free from its grasp. In later scenes, the octopus has all tentacles intact.
The Japanese army wears US camouflage uniforms and (obviously) plastic "airsoft" M16 rifles. The modern Japanese military has its own indigenous camouflage uniform and battle rifle. Japanese soldiers "at arms" wear either duty hats or helmets.
The Megalodon attacks the starboard side of the Iowa Class battleship at impossible speeds. However, the ship fires its main guns (a digital effect) while aiming straight ahead. The guns are not aimed at the threat, and they don't recoil or show any of the blast effects of a main gun firing.