The Battle for Caen degenerated into battle of attrition during which the Anglo-Canadian forces were frustrated by determined German resistance. This fighting drew vital German units including the bulk of their armoured strength to the Caen sector, which facilitated Operation Cobra, the breakout further west by Lieutenant General Omar Bradley's U.S. First Army. Dempsey convinced Montgomery to allow him to make an attempt at a breakthrough using three armoured divisions, assisted heavy bombers dropping of bombs. The result was Operation Goodwood. The result was a costly advance. Goodwood did succeed in its subsidiary aim of drawing away German reserves from Bradley's front: by 25 July, the Germans had 600 panzers, including all the heavy battalions with Tiger I and Tiger II tanks, opposite the Second Army and just 100 facing the U.S. First Army. But there was no denying that Goodwood had been oversold. There were calls for Montgomery to be sacked, although this was never likely, but little criticism of Dempsey despite him being the architect and directly responsible for some of its tactical flaws. Montgomery took all the heat upon himself, and never tried to shift the blame onto Dempsey.