During World War II, De Beers's control over rough diamonds carried consequences beyond engagement rings and luxury jewelry. Industrial diamonds were essential for precision cutting, drilling, and other military manufacturing processes, making access to them strategically important. Ernest Oppenheimer, who controlled De Beers during the war years, was later accused of restricting the release of industrial diamonds needed for the United States war effort. The allegation was advanced by former CIA director Admiral Stansfield Turner, who argued that De Beers's supply-control practices may have obstructed American access to a critical wartime material.
The charge remains disputed rather than established as a proven criminal case in the source record. It nevertheless reveals the extraordinary geopolitical reach of De Beers's monopoly: a private diamond company could influence not only consumer prices but also the availability of an industrial resource during a global conflict. The controversy compounded existing concerns about cartel behavior and secrecy around De Beers's stockpiles, while later histories of the company continued to portray its wartime dealings as part of the darker side of its effort to maintain scarcity and market control.
