Compartmentation had to buy evacuation time

Titanic's transverse bulkheads were limited by their height and the absence of longitudinal subdivision. Once the bow settled far enough, water could spill over the bulkhead tops and advance through the ship. Bulkheads reaching the main deck, supported by watertight decks and sensible internal routes above the machinery spaces, could have restricted flooding and prolonged survivability. The practical measure of the design was how much time the hull could provide for an orderly emergency response. No arrangement could make the ship literally unsinkable.