artillery to neutralise the German defences was a sound tactic, but the German forces were disposed in greater depth than had been encountered hitherto and the bombardment did not reach far enough. So too was the use of artillery to suppress the anti-tank defences, but it was less effective against the armoured self-propelled guns that the Germans were now employing. Montgomery took all the heat upon himself, and never tried to shift the blame onto Dempsey. On 2 August, Dempsey told Montgomery that he was fed up with Bucknall, the XXX Corps commander, and Major-General George Erskine, the commander of the 7th Armoured Division, and wanted to relieve them both. Relief of a corps commander is always a sensitive matter, and Bucknall had been appointed at Montgomery's request despite Brooke's reservations. Montgomery now had to admit to Brooke that he had made a mistake, and that Bucknall was not fit to command a corps in mobile operations after all. Bucknall was replaced by Horrocks. Erskine was also replaced, in his case by Major-General Gerald Lloyd-Verney. This meant that three of the four British corps commanders in the 21st Army Group had commanded a corps before Dempsey had, but Horrocks (XXX Corps) and John Crocker (I Corps) had been wounded, O'Connor (VIII Corps) had been a prisoner of war; the fourth, Ritchie (XII Corps), had been commander of Eighth Army before being demoted after losing the Battle of Gazala in June 1942. Horrocks wrote of Dempsey: The Second Army then made a rapid advance across northern France into Belgium, liberating Brussels on 3 September and Antwerp the following day, Dempsey's Tac HQ moved five times, covering in eleven days. Second Army took part in Operation Market Garden, the attempt to secure an early crossing of the Rhine. Dempsey believed that it was unlikely to succeed and openly questioned Montgomery. Dempsey suggested an alternative plan of crossing the Maas near Venlo and the Rhine at Wesel, closer to Bradley's American armies. According to Dempsey, Montgomery's mind was made up by a signal from London concerning the launching of German V-2 rockets against London from sites in the Netherlands. Montgomery's arguments were rooted in military strategy, which was his responsibility, whereas Dempsey's were based in the operational level of war, which was his. And too, Montgomery was difficult to argue with because he always employed well-reasoned military logic, and would not be swayed