From Richard Atkinson: The Guns at Last Light:
No liberated city in Europe was more important to the Allied cause than Antwerp. By the mid-sixteenth century it had become the richest town on the Continent, surpassing even Venice and Genoa, with a hundred or more ships at anchor every day, carrying spices from Portugal, grain from the Baltic, silk embroideries from Italy. The Inquisition, a Spanish pillage, and the rise of Holland cost the city its prosperity; not until the nineteenth century did Antwerp ascend again to become a bustling hive of diamond-cutting, cigar-rolling, sugar-refining, and beer-brewing. By the 1930s it ranked with Hamburg, New York, and Rotterdam among the world’s finest ports, handling a thousand ships each month, with twenty-nine miles of quays, more than six hundred cranes, nine hundred warehouses, and a vast rail yard.
All this was recovered whole on September 4. One early-twentieth-century estimate had calculated that the city’s defenses “would require an army of 260,000 men to besiege it effectually, and at least a year to reduce it by starvation.” The British had needed but a few hours. The capture of Antwerp and the exploitation of its port had been stressed since the earliest Allied invasion plans in December 1941. Eisenhower in a message to Montgomery on August 24 reiterated the need “to get a secure base at Antwerp,” an order repeated in a formal directive to commanders on August 29 and September 4. Montgomery echoed the supreme commander, stating his intent “to capture Antwerp,” as well as “to destroy all enemy forces in the Pas de Calais and Flanders.”
But Antwerp had a topographical quirk that required more than simply seizing the docks and the monkey house. Communication with the North Sea from the port required control of the eighty-mile estuary at the mouth of the river Scheldt, including fortified Walcheren Island on the north side of the Scheldt, and the polders around Breskens on the southern bank. Having sailed these waters in war and in peace for centuries, the Royal Navy was intimately familiar with the estuary. Four thousand British troops had died of fever on Walcheren during a campaign in 1809, with the survivors evacuated ignominiously to England. Churchill himself, as first lord of the Admiralty, had rushed to Antwerp in October 1914 to rally the Belgian government in defense of the port.
Admiral Ramsay on September 3 sent a telegram to SHAEF, with a copy to Montgomery, reminding all that “both Antwerp and Rotterdam are highly vulnerable to mining and blocking. If enemy succeeds in these operations, the time it will take to open ports cannot be estimated.” The first sea lord, Admiral Andrew Browne Cunningham, told his diary on September 7: “Again impressed on the [Combined Chiefs of Staff] that Antwerp, though completely undamaged, was as much use as Timbuctoo unless the entrance and other forts were silenced and the banks of the Scheldt occupied. I fear this is being overlooked by the generals.”
Alas, yes. An Ultra intercept of a Führer order on September 3, stressing the “decisive importance” of holding the Scheldt, was disregarded by Allied commanders; so were subsequent orders from Hitler, including an intercepted message reminding Fifteenth Army that “it must be insured that the Allies cannot use the harbor for a long time.” This “incomprehensible” error, the historian Ralph Bennett later concluded, was “a strategic mistake of such magnitude that its repercussions were felt almost until the end of the war.” Eisenhower’s messages to his top commanders about Antwerp had not specified capturing the Scheldt, and neither Montgomery nor Dempsey, the Second Army commander, attended the issue. Montgomery believed the enemy army’s position was hopeless. “The bottle is now corked,” he declared, “and they will not be able to get out”...