very bottom of the ship and extended right up to the top side.
The openings in the bulkheads were just about the size of the
ordinary doorway, but the doors did not swing as in a house,
but fitted into water-tight grooves above the opening. They
could be released instantly in several ways, and once closed
formed a barrier to the water as solid as the bulkhead itself.

In the Titanic, as in other great modern ships, these doors
were held in place above the openings by friction clutches.
On the bridge was a switch which connected with an electric
magnet at the side of the bulkhead opening. The turning
of this switch caused the magnet to draw down a heavy weight,
which instantly released the friction clutch, and allowed the
door to fall or slide down over the opening in a second. If,
however, through accident the bridge switch was rendered useless
the doors would close automatically in a few seconds.
This was arranged by means of large metal floats at the side
of the doorways, which rested just above the level of the
double bottom, and as the water entered the compartments
these floats would rise to it and directly release the clutch
holding the door open. These clutches could also be
released by hand.

It was said of the Titanic that liner compartments could be
flooded as far back or as far forward as the engine room and
she would float, though she might take on a heavy list, or
settle considerably at one end. To provide against just such
an accident as she is said to have encountered she had set back
a good distance from the bows an extra heavy cross partition
known as the collision bulkhead, which would prevent water