In May 1940, the UK launched two separate missions to steal Amsterdam’s stockpiles of industrial diamonds out from under the nose of the Nazi war machine.

The German Blitzkrieg campaign in the spring of 1940 utterly overwhelmed the Western Allies. The Wehrmacht’s modern mobile operations paralyzed the defenders, who tried to fight the war as if it were still 1918. The collapse was so complete that the evacuation from Dunkirk was, and still is, viewed as the single salient Allied triumph of the entire campaign. The rescue of hundreds of thousands of British troops from the beaches of northern France can hardly be called a “victory,” particularly as they left much of their equipment behind. 

Still, smaller successes occurred, which combined to impact the war in ways that were not immediately apparent.

Nazi Germany’s forces unexpectedly invaded the Netherlands on May 10. The Dutch had remained neutral during World War I, and intended to remain neutral again; they had a small army and were unprepared for war. Even so, they were able to force a brief stalemate along the New Meuse River at the city of Rotterdam. But the country’s fall to the far stronger invading forces was inevitable—within days, if not hours—and everyone knew it.

German control of the Netherlands was concerning to the Western Allies for several reasons. A successful German invasion would secure Germany’s right flank for an attack on France, as well as provide forward air bases from which to strike France and the United Kingdom. It would also give the German Kriegsmarine direct access to the North Sea, from which it could more easily sortie its U-Boat fleet. 

But less obvious advantages alarmed some in the Allied camp. In particular, the city of Amsterdam was a hub of the international gem trade, and thus home to large stocks of industrial diamonds. World War I had driven home the importance of manufacturing in modern war, and industrial diamonds are crucial to many manufacturing processes. 

Diamonds possess unique qualities beyond their desirability as gemstones. Those qualities include extraordinary hardness, thermal conductivity, and certain optical characteristics which make them indispensable in cutting, grinding, drilling, and use in advanced technology like radar. The German war economy would benefit enormously from capturing those industrial diamond stocks.

Dutch Diamond Traders Willingly Turned Over Their Stocks to the British

Aware of the danger, two British diamond merchants, Jan Smit and Walter Keyser, alerted the British government of the danger of a Nazi seizure of diamond stocks in Amsterdam, and offered to retrieve as many diamonds as possible from the city before its inevitable fall. Smit had numerous contacts in Amsterdam through his father, who was a major diamond trader there.

The problem was that Smit and Keyser had no way to get to Amsterdam, which was by then a war zone. Overwhelmingly, Dutch notables were attempting to flee the country to safety in the UK; trying to enter the Netherlands ahead of the inevitable Nazi occupation was like trying to enter a burning building minutes before its collapse.

The solution came from Winston Churchill himself, in an amazing circumvention of government red tape. The recently-appointed British prime minister—who had taken office on May 10, only two days before—personally approved the mission, providing a Royal Navy destroyer, HMS Walpole, to carry Smit and Keyser to Amsterdam. On the night of May 12–13, 72 hours after the Nazi invasion of the Netherlands began and only days before Amsterdam’s fall, the Walpole navigated a narrow gap between British and German minefields—narrowly avoiding a collision with the destroyer HMS Hereward, which was evacuating Queen Wilhelmina in the other direction.

Walpole put Smit and Keyser ashore at the Dutch coastal port of IJmuiden, up the canal from Amsterdam, some 19 miles away. The two men made their way to the city and contacted the elder Smit. They spent May 13 collecting large quantities of diamonds from various traders—all while dodging Dutch police and soldiers who were trying to contain pockets of German paratroopers, some of whom were dressed in Dutch uniforms. Gunfire was heard during several of Smit and Keyser’s meetings that day.

Most of the traders refused to take receipts from Smit and Keyser, not wanting to leave a paper trail when Nazi inspectors arrived. It has been noted that many of the traders were Jewish and could have used their supply of diamonds as a bargaining chip, turning them over to the Nazis in order to ensure safe passage out of the country. There is no evidence, however, that any did so. Instead, they prioritized the Allied war effort over their own well-being. That courageous and selfless decision was often a fatal one; many of the Jewish diamond traders in Amsterdam ultimately perished in the Nazi concentration camps during the Holocaust.

The British Ran a Parallel Safecracking Effort in Amsterdam

The effort encountered an obstacle, however, that prevented a complete success. Monday, May 13 was a bank holiday, and many vaults could not be opened until Tuesday morning. Smits and Keyser did not have until Tuesday morning. That problem was partially overcome when another British agent, Lt. Colonel Montagu Chidson, cracked into the huge vault at the Amsterdam diamond mart, liberating a large quantity of diamonds—even as German paratroopers were breaking into the building on a lower floor.

That evening, Chidson, who was unknown to Smits and Keyser and never met them, escaped the city as the two British diamond traders returned to IJmuiden to rendezvous with the Walpole. Their escape was not without some drama: carrying the diamonds in a large canvas bag, the men had to force a tugboat captain at gunpoint to ferry them to the destroyer in the harbor.

Smit, Keyser, and Chidson all returned safely to London, turning their prized diamond stocks over to the government. Smit and Keyser’s haul was kept in a London vault until after the war, and Chidson’s diamonds were delivered to Queen Wilhelmina. 

Back in the Netherlands, the German Luftwaffe broke the stalemate at Rotterdam on May 14 by controversially carpet-bombing the city center. The attack destroyed the entire area and killed nearly 900 people. The Germans threatened to do the same to the city of Utrecht if the Dutch continued their resistance. The Netherlands’ small air force was already destroyed, giving them no way to resist such a bombardment. Seeing that the situation could not be salvaged and wishing to spare the lives of their people, Dutch military leaders surrendered on May 15, beginning four years of Nazi occupation. 

The operation to save the diamonds was remarkable in its speed, execution, and daring, threading a needle into a very small hole to achieve its ends. Given the chaos of May 1940 and the logistics necessary to bring it off, Smit and Keyser’s bold foray into Amsterdam is among the more astounding stories from World War II. 

About the Author: William Lawson

William Lawson is a military historian focusing on World War II and 20^th century conflicts and the American Civil War. His specialty is operational level warfare, especially American amphibious doctrine. He writes on history, politics, and firearms for multiple publications and historical journals. He serves on the editorial advisory board for the Saber & Scroll Journal and Military History Chronicles and is a member of the Society for Military History and the American Historical Association. Lawson is based in Virginia.

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