It was with these machines--employed in mass formation--that the Germans attempted their great bombing operations in the Autumn of 1917, notably the expedition in November, when in a single night seven groups of airplanes made successive attacks on English cities; also the raid of Dec. 19 on London, when twenty machines took part in the attack on London and caused serious damage, including the work of an incendiary bomb that set fire to a factory and burned it to the ground. It is with these machines which they are still improving, and which they are multiplying by the bold creation of series, that the Germans have vainly sought to hold command of the air during their offensive in Picardy. The example and threat of the enemy had their effect in France. The French bombarding groups, which, born at the end of 1914, had in 1915 achieved famous flights into the heart of Germany, were compelled, with the advent of aerial combats, to renounce daylight operations, as these had become impossible or too uncertain for their slow and heavy machines, insufficiently armed, and had turned their attention to perilous night expeditions. But, despite successful raids and effective destruction, the French bombing operations remained more or less unsatisfactory. In the course of 1917 the use of the flying squadrons was finally adapted to the diverse needs of the battle front. In the French offensive at Verdun, while tactical aviation guided the waves of assault, regulated the artillery fire, and furnished information to the General Staff, while the swift airplane chasers, by a vigilant barrage, prevented all observation by enemy machines, the bombarding groups daily took part also in the action by hurling flames and destruction on railway stations, munition depots, storehouses at the rear, and sowing panic among the troops that were preparing to attack. Equipped at length with machines that combined the indispensable characteristics of speed, power, and armament, enabling them to hold the air in daytime, the French bombardiers attacked arsenals in the interior of Germany, and the British war dispatches of Dec. 25 mentioned a daylight raid of allied air squadrons upon Mannheim, where several fires followed, with heavy explosions at the central railway station and in the factories. The night groups, which had long made their raids only by moonlight, at length grew accustomed to flying in complete darkness. They multiplied their expeditions against enemy cantonments, railways, aviation fields, factories, and military and industrial centres. The task that remained at the opening of the Spring of 1918 was the fuller co-ordination of the groups of bombardiers.