Character mistake: At the beginning of the movie, Bill Paxton is pulling out documents out of the safe, maybe destroying some of them. Extremely unprofessional from an archaeological perspective. Although he represents a private company on a Russian ship searching for a diamond, he for sure violates many international laws with this brutal act of recovering objects. A professional treasure hunter should know that, plus a camera is filming him. He risks never getting a licence for a treasure hunt again.
Factual error: When Jack goes up to first class on a Sunday morning, the group is singing the Navy Hymn "Eternal Father." What is impossible is that they are singing the verse written for Aviators. The verse starts "O Spirit, whom the Father sent." They are singing the whole stanza continuing with "to spread abroad the firmament; O Wind of heaven, by thy might; Save all who dare the eagle's flight, And keep them by thy watchful care." The last line "From every peril in the air" can only be heard in the background as Jack is arriving on the scene. The Wright Brothers flew about 8 years before, and this verse was not added until the late 1930s. (01:11:00)
Revealing mistake: Towards the end of the film when Titanic is gradually getting higher Rose and Jack finally make it to the top of the ship, watch closely at the shot when they approach the top of the ship and Rose grabs onto Jack. In the background right at the very top of the shot you can see many green screens stood at the top of the ship in the background where people are running around. (02:30:00)
Factual error: Rose turned left after exiting the elevator during the search for Jack during the sinking. In the real Titanic, there was a wall to the left of the elevator in E Deck. In addition, going left from the elevators would take her to the port side of the ship, but the corridor outside the cabin where Jack is is on the starboard side. (01:53:40)
Revealing mistake: When the [CGI] Titanic leaves the dock, watch a man in a green jacket close to the bottom part of the screen. He is waving goodbye to 'nowhere', for that part of the boat is empty and its prow is pointing away from where he is staring. This reveals he was looking at a green screen, with no idea whatsoever of what was going on. (00:25:40)
Continuity mistake: Ruth walks to the ship, followed by Rose and Cal. When she is about to enter, the angle cuts and suddenly several women with dogs haven taken her place, followed by a lady who looks nothing like Ruth. Then in the following close-angle the group is meters behind from where they first were, repeating the walk towards the door. (00:22:15)
Factual error: Shortly after Old Rose mentions just leaving the coast of Ireland, a shot of the captain's area (with the steering wheels) is shown with the sun shining in from the right (if facing toward the front of the ship) This would be impossible for a westbound ship in the middle of the day as the sunshine could not enter from the north side of the ship. The rest of the movie has all scenes with the sun correctly coming from the south during mid-day as the ship is travelling westbound.
Other mistake: The ship is down by the bow about 30°. There follow scenes in which people make their way through flooded passageways. The water is chest-high, but level.
Continuity mistake: When Jack and Rose are in the lower hallway after escaping from Cal, Titanic is already at a major tilt with the bow completely underwater and the first class dining saloon getting flooded. The problem is that the water in the hallway is completely level and the water that floods is also level. With the ship tilted the way it is the water should have been collecting at the end of one of the hallways, not flat.
Continuity mistake: Just after Rose leaves Cal, we get an underwater shot panning down on Jack, showing that the window he's standing next to is fully submerged. However, interior shots after that show air around the upper edge of it. It's not trapped air: it's constantly bouncing around, in a wave-like pattern. (01:53:10)
Continuity mistake: In the "You jump, I jump" scene with Jack and Cal persuading Rose to get on a lifeboat, Rose embarks the lifeboat at the front, port(left side) side of deck top. Yet when Rose jumps back on the ship, she climbs back on in the middle, starboard(right side) of A deck where the windows change, running towards the bow to the Grand Staircase; while Jack is running towards the Stern from the Port front side of deck top. Jack enters the Grand Staircase from the port side of Deck top, and Rose enters the Grand Staircase from the port side of A Deck. (02:11:40)