to resign on 17 May, showed the apprehensions of the German high command about the speed of movement and vulnerability of the XIX Panzer Corps. Doughty suggested that the development of the Manstein Plan showed that the force sent through the Ardennes was intended to follow a familiar strategy of intended to encircle and annihilate the Allied armies in (cauldron battles). Twentieth-century weapons were different but the methods were little changed from those of Ulm (1805), Sedan (1870) and Tannenberg (1914). When German forces broke through on 16 May, they did not attack French headquarters but advanced westwards in the manner of a cavalry raid. Doughty wrote that Fuller had called the advanced forces of the German army an armoured battering-ram, covered by fighters and dive-bombers acting as flying field artillery, to break through a continuous front at several points. The XIX, XLI and XV panzer corps had operated as the leading force through the Ardennes but the most effective Allied resistance to the south and south-west of Sedan was reduced by the combined operations of infantry, tanks and artillery, a fact overlooked for long after 1940. bombers had not acted as flying artillery and their main effect occurred on 13 May, when bombing collapsed the morale of the French 55th Division. Air attacks helped the ground forces to advance but destroyed few tanks and bunkers, most of which were taken by the skill and determination of German infantry, sometimes helped by anti-tank guns, accompanying guns and a few tanks. Fuller's writing was in the vein of much of the early reports of the Battle of France but since then new studies had added nuance, dwelling on the complications and chaos of the military operations. The Manstein Plan led to much more than a simple tank rush through the Ardennes and the fields of northern France; the toughness and training of the German infantry should be recognised, along with the efforts of the engineers and artillery, which got the XIX Panzer Corps across the Meuse. Doughty also wrote that the success of the German army could not adequately be explained without reference to French mistakes. French strategy was unusually vulnerable to an attack through the Ardennes; operationally, French commanders failed adequately to react to the breakthrough of massed panzer forces. Tactically, the Germans were often able to overcome French defences that usually were inadequate. French military intelligence failed to predict