The Canadian Division sailed from England and landed in France in February 1915, and was briefly initiated to trench warfare on the periphery of the Battle of Neuve Chapelle in March 1915, before being attached to the British 2nd Army, under the command of Sir Horace Smith-Dorrien, in the Belgian town of Ypres. It was in front of Ypres on 22 April 1915 that the Canadians bore the brunt of the opening by the Imperial German Army of the 2nd Battle of Ypres, presaged by the first use in history of poison gas as a military weapon. At 5.00 pm the Germans began heavily shelling the French trenches adjoining the Canadian Division's sector, and the Canadians and the French Algerian troops stationed next to them saw a fog traveling across no-mans land towards their positions, which also concealed the advance of German forces behind it wearing gas masks. The fog was chlorine gas. The Algerians broke and fled, suffering over 6000 casualties in a matter of minutes, and the Canadians were consequently forced to defend twice the length of the front line they had vacated. Although the Canadian Division held on for more than two days, ground was lost to the attacking Germans, and the Canadian Division suffered over 50% casualties (nearly 6,000 troops).