[RMS] Titanic received a series of warnings
from other ships of drifting ice
in the area of the Grand Banks of Newfoundland,
but Captain Edward Smith ignored them. 

the ship continued to steam at full speed,
which was standard practice at the time.

First Officer William Murdoch ordered the ship
to be steered around the obstacle and
the engines to be reversed, but it was too late;
the starboard side of Titanic struck the iceberg,
creating a series of holes below the waterline. 

The hull was not punctured by the iceberg,
but rather dented such that the hull's seams
buckled and separated, allowing water to rush in. 

It was long generally believed the ship sank in one piece;
but the discovery of the wreck many years later
revealed that the ship had broken fully in two. 
—Titanic, wikipedia.org