The relative positions of the Armies in 1915 altered little from those
taken up after the battle of the Marne, but there were many historic
events during that trying year--the capture by the British of Neuve
Chapelle, the two battles of Ypres (in the second of which the Germans
introduced poison gas), the heavy campaigning in the Argonne, the
bombardment of Rheims, the French offensive in Champagne, and the
British offensive at Loos.
During the winter of 1915-1916 Germany’s initial hopes of success
began to grow less rosy. The British Army continued to grow; Italy
and Rumania joined the Allies; and on almost every side the Central
Powers began to feel pressure. The outstanding events during this
period included the smashing by the British of an onslaught from
Messines Ridge and the repulsing of an advance towards Albert. There
was terrific fighting at Verdun (where the French displayed heroic
qualities), and the great Allied offensive on the Somme. There was
also a British victory on the Ancre, and “tanks” made their initial
appearance.