By September 1944, Allied forces had successfully broken out of their Normandy beachhead and pursued shattered German forces across northern France and Belgium. Although Allied commanders generally favoured a broad front policy to continue the advance into Germany and the Netherlands, Field Marshal Bernard Montgomery proposed a bold plan to head north through Dutch Gelderland, bypassing the German Siegfried Line defences and opening a route into the German industrial heartland of the Ruhr. Initially proposed as a British and Polish operation codenamed Operation Comet, the plan was soon expanded to involve most of the First Allied Airborne Army and a set-piece ground advance into the Netherlands, codenamed Market Garden.