required was that these fronts stand firm while the Germans won in the west, where now they outnumbered their opponents. He firmly believed that his opponents could be crushed by battlefield defeats regardless of their far superior resources. Offensive tactics were tailored to the defense. Their opponents were adopting defense in depth. He would attack the British because they were less skillful than the French. The crucial blow would be in Flanders, along the River Lys, where the line was held by the Portuguese Army. However, winter mud prevented action there until April. Consequently, their first attack, named Michael, was on the southern part of the British line, at a projecting British salient near Saint-Quentin. Schwerpunkts would hit on either side of the salient's apex to pocket its defenders, the V Corps, as an overwhelming display of German power. Additional troops and skilled commanders, like von Hutier, were shifted from the east. Army Group von Gallwitz was formed in the west on 1 February. One quarter of the western divisions were designated for attack; to counter the elastic defense, during the winter each of them attended a four-week course on infiltration tactics. Storm troops would slip through weak points in the front line and slice through the battle zone, bypassing strong points that would be mopped up by the mortars, flamethrowers, and manhandled field guns of the next wave. As always surprise was essential, so the artillery was slipped into attack positions at night, relying on camouflage for concealment; the British aerial photographers were allowed free rein before D-day. There would be no preliminary registration fire; the gunners were trained for map firing in schools established by Bruchmüller. In the short, intense bombardment each gun fired in a precise sequence, shifting back and forth between different targets, using many gas shells to keep defenders immersed in a toxic cloud. On D-day, the air force would establish air supremacy and strafe enemy strong points, and also update commanders on how far the attackers had penetrated. Signal lamps were used for messaging on the ground. Headquarters moved close to the front and as soon as possible would advance to pre-selected positions in newly occupied ground. OHL moved to Spa, Belgium while Hindenburg and Ludendorff were closer to the attack at Avesnes, France, which re-awoke his memories of occupied France 41 years before. Breaking the trench stalemate Operation Michael began on 21 March.