Factual error: The Iowa is sailing with a depleted crew, one that most likely has no experienced gunner's mates. The 16-inch turret requires a 79-man crew to operate it, and can fire a salvo every 30 seconds. Despite these handicaps, the minimal crew in the movie was firing salvos every few seconds.
Factual error: The museum girl locates crates down in the bowels of the Iowa, each with two 16-inch shells, weighing around 2700 pounds apiece, inside. The crates, made of relatively thin planking, would never support that weight, and the crew was depicted transporting them across the deck, presumably to feed them through the crew hatch under the turret overhang.