When Germany began its assault on Holland on May 10, 1940, the international community was not just worried about the lives of the Dutch people but also about the massive stocks of industrial diamonds in Amsterdam.
Industrial diamonds were used for many manufacturing purposes and the country that controlled the diamonds could create more weapons, vehicles, and sophisticated technology like radar.
That's why two diamond traders in England, Jan Smit and Walter Keyser, offered their services to the British government. Jan's father ran a large trading interest in Amsterdam and was friends with many more traders. Smit was certain that if he were allowed passage into and out of Amsterdam, he could get many diamonds out before the Nazis could seize them.
Approval for the mission went all the way to the new prime minister Winston Churchill himself. Churchill ordered a military officer to escort the two men and granted them the use of an old World War I destroyer, the HMS Walpole, to get them into the city. The Walpole had to thread a mile gap between German and British minefields at night under blackout conditions to get across the English Channel.
During the transit, the Walpole almost struck another British ship sneaking through the darkness. Those on the Walpole would learn years later that the other ship was evacuating members of the Dutch Royal family.
Keyser and Smit arrived in the harbor just before daybreak and spent the day working with Smit's father to convince traders to release the diamonds to the Keyser and Smit. From their landing at the docks to their trips around the city, the men were driven by a Jewish woman, Anna, who protected them from possible German spies.
Throughout the men's day in Amsterdam, Dutch police and soldiers were attempting to root out pockets of German paratroopers wreaking havoc in the city. Across the country, German forces were quickly taking over and quashing resistance. Gunfire interrupted a few of their meetings.
Many of the diamond traders were Jewish and could have bribed their way out of the country with their stocks and possibly escaped the Holocaust. Instead, they took the chance to get them away from German hands. Most of the traders even refused receipts out of fear that the Germans would learn how many diamonds they had prevented the Third Reich from getting their hands on.
While the men gave many of their diamonds to the English agents, the attack had come during a bank weekend and many were in safes that couldn't be opened for another day or more.
Luckily another British agent, Lt. Col. Montagu R. Chidson, made his way to the massive vault at the Amsterdam Mart and spent hours breaking into it, even as German paratroopers forced their way into the building. He escaped with the diamonds as the soldiers forced their way down the stairs.
At the end of the day, Chidson escaped on his own while Anna rushed Smit, Keyser, and their military escort back to the docks just in time to rendezvous with the HMS Walpole. Smit carried a thick canvas bag filled with the diamonds and forced a tug driver at gunpoint to take them to the British destroyer.
Chidson's diamonds made their way to Queen Wilhelmina while the diamonds recovered by Smit and Keyser were held in London for the duration of the war.
(h/t David E. Walker for his 1955 book, "Adventure In Diamonds" where he recounts much of the first-hand testimony of the men who took part in the operations to recover diamonds ahead of the Nazi advance).