Off the Atlantic coast of southwestern Africa, a converted heavy-lift ship called the Dock Express 20 hunts for diamonds on the seabed. Originally built for hauling oversized industrial cargo, the vessel has been reengineered into a floating mining platform for De Beers, lowering crawler machines hundreds of feet down to scrape up diamond-bearing gravel and pumping it aboard through massive hoses for sorting. The film follows the crew as they run this operation in rough seas, strong currents, and the unpredictable weather typical of the region, showing the mechanical systems that separate stones from sediment and the engineering that keeps the ship stable while dredging. It is part of the World's Toughest Ships series, which profiles vessels adapted for extreme industrial jobs, and this episode treats the Dock Express 20's transformation from cargo carrier to mining rig as the real story, alongside the logistics of pulling a fortune in gemstones from a seabed nobody can see.