Titanic is about 12,500 feet deep.
Pressure at that depth is roughly 5,500 psi. As others have said, hull failure at that pressure would have been instant death.
There's some old video, probably from the 1930s, of testing of a deep sea tethered bathysphere.
It leaked and filled with water (no one was aboard, apparently).
AH! Here we go, an account of it from Wikipedia...
"When conducting an unmanned test of the Bathysphere with the third window installed, they found it almost entirely full of water. Realizing the immense pressure that the Bathysphere must be under, Beebe ordered his crew to stand clear and began loosening the hatch's bolts to remove the hatch himself.[2] Beebe described the experience that followed this in his book Half Mile Down:
Suddenly, without the slightest warning, the bolt was torn from our hands, and the mass of heavy metal shot across the deck like the shell from a gun. The trajectory was almost straight, and the brass bolt hurtled into the steel winch thirty feet [9.1 m] away across the deck and sheared a half-inch [13 mm] notch gouged out by the harder metal. This was followed by a solid cylinder of water, which slackened after a while into a cataract, pouring out the hole in the door, some air mingled with the water, looking like hot steam, instead of compressed air shooting through ice-cold water.[6]
After replacing the third window with the steel plug and conducting another unmanned test, the same problem happened again.[2] Beebe later described what would have happened to him and Barton had they been inside the sphere on a dive during which it leaked. They would not have had time to drown: due to the immense pressure, "the first few drops of water would have shot through flesh and bone like steel bullets."[8]"
