Visible crew/equipment: Watch the special edition version of the movie. During the scene when the crane is falling down on top of the sub, the camera is following people around the passages. When it comes to the end of a hall, and a hatch is shut in our face, we can see the shadow of the camera equipment in the door. (00:54:13)
Continuity mistake: When Linds says "I got it. It's headed straight for us," Bud looks out the front window. Watch the umbilical because it doesn't start to move until a split second after the camera is in full frame. (00:54:55)
Revealing mistake: After the water tentacle sequence, Coffee brings Schoenick back to their bunks to get the submachine gun, so they can take over the rig. The bag containing the gun is stashed behind some pipes up by the ceiling. Watch when he reaches behind the pipes to grab the bag--the pipes move at least six inches. (01:31:57)
Revealing mistake: When he's on his way to send the nuke down the abyss, Coffee leaves the other SEALs to guard the rig's crew in the kitchen. He goes through a door, locks it and secures it with his belt, and then bangs on it to test its security. It moves more than a metal door in a metal housing would. (01:37:43)
Continuity mistake: Bud swims to the moon pool and tries to sneak up on Coffey. Coffey aims a gun at Bud. Bud's right eye is swollen. In the next scene its not, and the following scene it is. (01:43:35)
Plot hole: Granted, Coffee is suffering from "high-pressure nervous syndrome," but if you're a Navy SEAL, wouldn't you notice whether or not your pistol has a magazine in it? Monk pulls the clip out of his jacket and starts knocking rounds out of it for the rig crew's benefit; the same dramatic effect could have been achieved with a handful of cartridges he could let slip through his fingers. You could argue that Monk didn't have enough time to unload the gun and replace the magazine, but in that case, I think the scene where Monk briefly had the gun should have been a bit longer. (Even had the empty magazine been IN the gun, Coffee still might notice the difference in weight, but that would be easier to suspend your disbelief for.) (01:43:53)
Visible crew/equipment: During Bud and Coffey's fight in the lab, we see a lightbulb swinging from side to side between the two men. If you look closely, you can see a hand (belonging to a third person) pushing the lightbulb. The only people in the room are Bud and Coffey. (01:44:16)
Continuity mistake: Early in the film Bud throws his wedding ring down the latrine and then retrieves it with his right hand so it is covered with the blue disinfectant. In a (much) later scene, Bud has a blue right hand, despite not having had one in the intervening period. (01:44:48)
Continuity mistake: When Bud and Lindsay are in the sub after the big chase, water leaks in and Bud searches for something to fix it. He delivers some dialogue while opening (I believe) a first aid kit. The camera angle switches to Lindsay as she says something, and Bud can be seen in the background opening the kit once again. (01:54:44)
Continuity mistake: When Bud is giving his wife CPR and starts to slap and yell at her you see her blink and swallow before they have any life readings. You also catch her closing her mouth as if to wet it when he bends over her body. (02:03:50)
Continuity mistake: When Ed Harris gets used to the Liquid Breathing Suit you can see air still in his helmet after he goes in the water. That shouldn't be! The purpose of the suit is to get any remaining air out for it to work. (02:10:25)
Other mistake: When Ed Harris is dropping down the Abyss there are a couple of time that bubbles come out of his mouth or can be seen in his nostrils, even though he is supposed to have been breathing liquid for quite some time. (02:13:28)
Revealing mistake: When the Benthic Explorer is lifted out of the water, the left screw is wobbling in the wind, revealing that it's a model. (02:34:00)
Factual error: [Special Edition] The Statue of Liberty is incorrectly shown to be facing the Narrows bridge.
Other mistake: Near the beginning there is a scene where they are launching a submersible with Lindsey and the seal team in it. Lindsey waits until the sub is dangling over the water then pulls a lever and the sub drops about 10 feet into the water with a big splash. Several problems: 1) Those subs are hugely expensive. They put them in the water very gently. 2) Those subs are so expensive that they don't risk having a release mechanism as depicted. They use a standard screw shackle to ring and would have to have a swimmer let them go. 3) Due to the buoyancy of the sub, falling that far to the water would give all passengers back injuries due to the sudden deceleration when the sub hits the water.
Visible crew/equipment: During the scene where Bud and Lindsey are arguing about who will wear the scuba equipment back to the rig from their downed mini sub, a hand with a cloth wipes water off the camera. It's during the line when the camera is facing Bud and he says "Don't argue with me goddammit, just put it on." This is visible in the 4:3 version for TV, as well as the widescreen version on DVD.
Continuity mistake: When Bud leaves Jammer behind in the sub, he gives him a strand of rope to keep the two connected. At first Bud keeps the bundle of rope and hands Jammer the loose end, however in later scenes it's shown that Jammer holds the bundle of rope and Bud holds the loose end; as Jammer is feeding him line.
Continuity mistake: When Lindsay is pulled from the pool after she drowns her wet hair is covering her face. In the next shot she is laying on the floor and Bud is smoothing her hair back to give her CPR. The shot changes again and her hair is back covering her face like it was when they pulled her from the water.
Continuity mistake: When Bud sneaks on Coffey in the moon pool, they are seen fighting. During this Bud shirt gets wet and rides up his back. In some shots it goes down again, but then goes right back up.
Other mistake: During the submarine interior scene, there are several dead seamen shown floating about. One of them is pretty close to the camera and floating with his eyes open. He blinks before the shot ends.
Suggested correction: They're on an emergency rescue mission and don't have time to be delicate with the equipment. Also, everyone in the sub is shown being thrown around when the sub hits the water. Hence the angry looks toward Lindsey.
They would still put the sub safely in the water. The first thing in priority in a rescue situation is scene and crew safety. If you damage the rescue sub or hurt the rescue team what's the point of the rescue. They would take the extra few minutes necessary to put the submersible safely in the water.