"PRACTICALLY UNSINKABLE"
As some people know, the Titanic and her sister ship Olympic were built with a cellular double bottom and divided into 16 major watertight compartments with 15
transverse watertight bulkheads that ran clear across the ship. These watertight bulkheads were labeled "A" through "H" and "J" through "O". (The letter "I" was not used.)
The first two and last six of these bulkheads ran as high as D deck while the middle seven ran as high as E deck. Titanic and Olympic were labeled a "two compartment
ship" because they could remain afloat with any two adjacent  watertight compartments completely open to the sea without in any way involving the safety of the ship. Since
no one could imagine anything worse than a collision near the juncture of two of the these compartments, these ships were often referred to as being "practically unsinkable."
Condition B0 - The first plan shows the ship in the unflooded condition with the waterline marked as a solid blue line.

Condition B1 - "The first thing was to flood the forepeak tank, that was the foremost compartment of the ship, which is marked in yellow, and which gave the yellow
waterline."

Condition B2 - "I then flooded No. 1 hold, which is tinted green, and I got the green waterline. That is No. 1 hold plus the forepeak."

Condition B3 - "I then, in addition to having the forepeak flooded and No. 1 hold flooded, flooded No. 2 hold, which is marked brown, and I got the brown waterline.
When No. 2 was flooded it would flood the firemen's passage, because, the waterline has then got above the step in the bulkhead and can go down the stairs. Of course,
as you will see, the water is still at that time below the level of the top of the bulkheads which run to the E deck."

Condition B4 - "Then, having flooded the forepeak and No. 1 and No. 2 holds, I also flooded No. 3 hold, which I then wanted to indicate by the red space which is
represented by the red line."

Condition B5 - "I then flooded No. 6 boiler room, in addition to the others, of course, which is shown in the blue tint, and gave the blue waterline. You will now see that
the water [from No.1 hold] had got up above the top of A bulkhead, and would get down into the rest of the forepeak. It means the eventual foundering of the ship."

Condition B6 - "I then flooded No. 5 boiler room in identically the same way as I had previously flooded No. 6, adding its flooding effect to the forward spaces, and I
got the black line, which, as you will notice, puts the forecastle entirely under water, and also the forward end of  B deck."

Condition B7 - The next was the partial flooding of BR 4 shown in dashed red. "The [dashed] red line is approximately parallel to the forecastle head, and it shows that
the stern is out of the water as far about as the base of the mainmast [the mast aft of the fourth funnel], or a little further forward."

If the wound came as far aft as BR 5, carrying the watertight bulkheads to D deck would not have saved the ship. If the watertight bulkheads were carried up to C deck
the ship might have been saved provided that there was no damage in BR 4. As Wilding said, "I believe that no bulkhead arrangement possible forward would have
saved the ship [in that instance], because of the red dotted line which I have drawn across [Condition B7] as the result of the earlier calculations."
Flooding By Compartment
In reality, the design was closer to a three compartment ship for the most part as can be seen by reference to the diagram below which shows the maximum number of
compartments that can be flooded in any given location without the ship foundering. These were derived from the ship's floodable-length curves which were published in
the 1997 RINA Transactions by Hackett and Bedford, "The Sinking of S.S. TITANIC - Investigated by Modern Techniques." The design of these vessels almost met a
three-compartment standard except for three conditions: flooding in hold 3 and boiler rooms 5 and 6, flooding in boiler rooms 4, 5, and 6, and flooding in both engine
rooms and the electric dynamo room. Other than these three conditions, the ship would remain afloat with any 3 adjacent compartments open to the sea.
Place your mouse over the picture below to view the watertight subdivision
of the Titanic. Click to learn about the role of the watertight doors.
At the British Inquiry into the loss of the Titanic, H&W's naval architect Edward Wilding presented a plan that he called "Flooding by Compartment." This plan was
developed to show how the Titanic would trim down by the head as individual compartments are flooded one at a time beginning with the first and working aft. It was used
solely to show how the waterline of the ship would change as subsequent compartments are allowed to flood to the waterline, and was used to show when water would
have overtopped the transverse watertight bulkheads if carried to various heights. It was not derived to demonstrate how the ship actually flooded as quite a few
misinformed people tend to believe. The animated sequence is shown below followed by the text that describes what was presented by Wilding.
Watertight Subdivision Changes to Olympic Following the Titanic
After the Titanic disaster, modifications were made to Olympic to improve her ability to withstand a
similar accident. To find out more about what these changes were, please go to:
MODIFICATIONS TO OLYMPIC