Clive Cussler's the Corsican Shadow

France, May 1940. As the German army blitzes Europe and Parisians flee their city, the chief curator of the Musee de l'Armee is ordered to take a mysterious piece of cargo out of the country. Arriving at the port of Le Havre, he learns his intended ship has been sunk, and his cargo's uncertain fate now rests on a decrepit steamer, sailing out under German fire.

Decades later, a diving expedition in the English Channel leads National Underwater and Marine Agency Director Dirk Pitt to a cache of uncut diamonds on a shipwreck. No sooner than they are discovered, the diamonds are stolen - and Pitt and the NUMA agency find themselves up against a murderous cabal with far more destructive plans than mere theft. Vital water treatment facilities around the globe are being targeted - placing the world's population in grave peril.

Book 27 in the Dirk Pitt series.