It wasn't until 1985, when the wreckage of the Titanic was discovered, that they found out the ship had broken in two while sinking. In this film, the Titanic does not break in two, but goes down in one piece with most of her decks intact.
The creaking noises during the sinking were created by the set as it was winched up to create the tilting deck effect. The microphones picked up the noises. Roy Ward Baker thought they added a huge amount of realism, as they sounded like the groaning noises a sinking ship would make, so he kept them in.
Lawrence Beesley, a survivor from second class, was on the set during filming. At one point, when the sinking was being filmed, he attempted to enter the scene and, perhaps symbolically, "go down" with the ship. Director Roy Ward Baker didn't allow this, as it would have been a union violation, which could have closed down production.
After the ship leaves Southampton and the caption "April 14" is seen, the shots of the Titanic and the passengers on deck were taken from Titanic - O Épico Nazista Banido (1943), a Nazi propaganda film.
Each page of the script was marked with the angle of the ship's deck at that point in its descent, to maintain accuracy and continuity when scenes were shot out of order.