Raise the Titanic! (Dirk Pitt #4) by Clive Cussler

The President's secret task force has developed an unprecedented defensive weapon that relies on an extremely rare radioactive element--and Dirk Pitt has followed a twisted trail to a secret cache of the substance. Now, racing against brutal storms, Soviet spies, and a ticking clock, Pitt begins his most thrilling mission--to raise from its watery grave the shipwreck of the century...