At 5 p.m. on April 22, 1915, the Germans released around 168 tons of chlorine gas, using the prevailing wind to carry the toxic cloud toward the French 45th and 87th Divisions at Gravenstafel. The gas worked far better than anticipated, creating chaos among the French, Moroccan and Algerian troops and opening a 7-kilometer (4-mile) gap in the defensive line. The Germans failed to effectively capitalize on the break; surprised by the effectiveness of the gas, they were unprepared to exploit the situation. For military planners on all sides, however, the apparent usefulness of poison gas had been proved. The main reason for the effectiveness of the first chlorine attack was that the troops on the receiving end did not know what they were facing.