The reason for raising the Titanic is to recover a very special radioactive mineral that is needed to provide the power for a missile defense shield. Without the mineral, there is no shield, hence, the government decides to raise the Titanic to get the mineral that Brewster supposedly was shipping back to the U.S. on the Titanic. After the Titanic is raised and the vault is opened, there is nothing in the vault but common rocks and Brewster's remains. Brewster actually buried the real mineral in a grave in Southby,England, hence the postcard "Thank God for Southby". In the movie, Dirk Pitt and Dr. Seagram decide to leave the mineral hidden in the grave, because someone might use it for a weapon rather than a missile defense shield. Robert H. Gibbons