Bavarian mountain warfare expert von Dellmensingen was sent to assess the Austro-Hungarian defenses in Italy, which he found poor. Then he scouted for a site from which an attack could be mounted against the Italians. Hindenburg created a new Fourteenth Army with ten Austro-Hungarian and seven German divisions and enough airplanes to control the air, commanded by Otto von Below. The attackers slipped undetected into the mountains opposite to the opening of the Soča valley. The attack began during the night when the defender's trenches in the valley were abruptly shrouded in a dense cloud of poison gas released from 894 canisters fired simultaneously from simple mortars. The defenders fled before their masks would fail. The artillery opened fire several hours later, hitting the Italian reinforcements hastening up to fill the gap. The attackers swept over the almost empty defenses and marched through the pass, while mountain troops cleared the heights on either side. The Italians fled west, too fast to be cut off. Entente divisions were rushed to Italy to stem the retreat by holding a line on the Piave River. Below's Army was dissolved and the German divisions returned to the Western Front, where in October Pétain had directed a successful limited objective attack in which six days of carefully planned bombardment left crater-free pathways for 68 tanks to lead the infantry forward on the Lassaux plateau south of Laon, which forced the Germans off of the entire ridge the French Army had recovered.