in early September and were secured by XXX Corps under the command of Lieutenant General Brian Horrocks. Montgomery halted XXX Corps for resupply short of the wide Albert Canal to the north of the city, which consequently remained in enemy hands. Horrocks regretted this after the war, believing that his corps might have advanced another with the fuel available. Unknown to the Allies, at that time XXX Corps was opposed by only a single German division. The pause allowed the Germans to regroup around the Scheldt River, and by the time the Allies resumed their advance, General Kurt Student's 1st Parachute Army had arrived and set up strong defensive positions along the opposite side of the Albert Canal and Scheldt river. The task of breaking the strengthened German line, which stretched from Antwerp to the North Sea along the Scheldt River, would fall to the First Canadian Army in the month-long, costly Battle of the Scheldt. The Allies "sustained 12,873 casualties in an operation which could have been achieved at little cost if tackled immediately after the capture of Antwerp. .... This delay was a grave blow to the Allied build-up before winter approached." The British historian Antony Beevor was of opinion that Montgomery, not Horrocks was to blame for not clearing the approaches, as Montgomery "was not interested in the estuary and thought that the Canadians could clear it later". Allied commanders were looking ahead to "leaping the Rhine...in virtually one bound." Despite Eisenhower wanting the capture of one major port with its dock facilities intact, Montgomery insisted that the First Canadian Army should clear the German garrisons in Boulogne, Calais and Dunkirk first, although these ports had all suffered demolitions and would not be navigable for some time. Boulogne (Operation Wellhit) and Calais (Operation Undergo) were captured on 22 and 29 September 1944; but Dunkirk was not captured until the end of the war on 9 May 1945 (see Siege of Dunkirk). When the Canadians eventually stopped their assaults on the northern French ports and started on the Scheldt approaches on 2 October, they found that German resistance was far stronger than they had imagined, as the remnants of the Fifteenth Army had had time to escape and reinforce the island of Walcheren and the South Beveland peninsula. Winston Churchill claimed in a telegram to Jan Smuts on October 9 that "As regards Arnhem, I think you have