Why did the Titanic actually sink?

The collision on the night of April 14, 1912 did not tear a single long gash, as long depicted. Sonar surveys of the wreck indicate the iceberg buckled the hull plates and popped rivets along roughly 300 feet, opening a series of relatively narrow gaps below the waterline. That was enough. The ship's watertight compartments could keep it afloat with four flooded; six took on water. Because the bulkheads did not extend high enough, water spilled over the tops from one compartment into the next as the bow sank, a progressive failure the design did not account for.

The contributing decisions matter more than the metallurgy debates about brittle steel and weak rivets, which remain contested and were probably marginal. The ship carried lifeboats for about half those aboard, which was legal under outdated regulations tied to tonnage rather than passenger count, and several boats launched well below capacity. Multiple ice warnings from other vessels were received and not acted on decisively, and the ship maintained high speed through a known ice field, which was standard practice at the time and is precisely what the disaster ended. The aftermath produced the International Convention for the Safety of Life at Sea, mandating lifeboat capacity for all aboard, 24-hour radio watch, and the International Ice Patrol, which still operates. The unsinkable claim, incidentally, was largely a press and post-disaster construction rather than an official White Star slogan.