Following the spring drive of the Allies on the western front and the retirement of the Germans to the so-called Hindenburg line, the British and French continued their offensive during the months of May, June and July, 1917, which concluded the third year of the great struggle. Great battles in the Champagne and along the Aisne were fought by the French, who in April had captured Auberive, and they advanced their forces from one to five miles along a fifty-mile front, inflicting great and continual losses on the enemy. At the end of the third year, the French line ran from northwest of Soissons, through Rheims, to Auberive. French troops also appeared in Flanders during this period and co-operated with the British on the left of Field Marshal Haig's forces. The chief command of the French armies was in the hands of General Petain, the gallant defender of Verdun, who was appointed chief of staff after the battle of Craonne. The continuation of the British offensive northeast of Arras, following the bloody battle of Vimy Ridge, which was firmly held by the Canadians against desperate counter-attacks, placed the British astride the Hindenburg line, and the Germans retired to positions a mile or two west of the Drocourt-Queant line. These they held as the third year closed at the end of July. In June, 1917, the British began an attack on Messines and Wytschaete, in an effort to straighten out the Ypres salient. By this time their flyers dominated the air, and they had gained the immense advantage of artillery superiority. By way of preparation, the British sappers and miners had spent an entire year in mining the earth beneath the German positions, and the offensive was begun with an explosion so terrific, when the mines were sprung, that it was heard in London. Following immediately with the attack, the British won and consolidated the objective ground, capturing more than 7,500 German prisoners and great stores of artillery. This victory placed them astride the Ypres-Commines canal, having advanced three miles on an eight-mile front. Portuguese and Belgian troops assisted in this offensive, which resulted in the greatest gain the Allies had made in Belgium since the German invasion. Fighting in this terrain had been confined for many months to trench-raiding operations. GERMAN LOSSES TO JULY It is estimated that during April, May, and June the Germans suffered 350,000 casualties on the western front. The totals of the German official lists of losses for the entire war to July 19, 1917, were as follows: Killed or died of wounds, 1,032,800; died of sickness, 72,960; prisoners and missing, 591,966; wounded, 2,825,581; making a grand total of casualties of 4,523,307. The German naval and colonial casualties were not included in this total. FURTHER GAINS IN FLANDERS