In other words, Vimy Ridge bears the same relation to Arras that Messines and its contiguous hills do to Ypres, but while the former ridge also flanks the great German salient stretching down to the Oise, the latter ridge flanks from the southeast the British salient at Ypres developed by the battle of Flanders. In this second phase of the great battle the German penetration, through military design or expediency, has so far been developed in the direction of Ypres; not in the direction of Arras. NUMBER OF MEN ENGAGED As to the number of men engaged on each side, experts at the front have been wide apart. It has been understood that Great Britain has in France 3,500,000 rifles, and that of these 675,000 were on the front when the attack began, thus (if these figures are correct) leaving an army of reserve and manoeuvre of 2,850,000, minus 150,000 men on leave in England. It was understood that the number of French rifles available on the Continent is between 4,000,000 and 5,000,000, of which 1,575,000 were at the front on March 21, leaving 2,425,000 for reserve and manoeuvre, which to the extent of 500,000 may have been available in the present battle, with the constant deploying of the French line in the south and the taking over of ten miles of the British line. [Illustration] [Illustration: MAP OF THE BATTLE OF PICARDY. THE CHAIN LINE ON THE EAST SHOWS BATTLE FRONT MARCH 21, 1918. SHADED SPACE INDICATES GERMAN GAINS UP TO APRIL 17. BROKEN LINE SHOWS NEW FRONT AT THAT DATE. INTERVENING LINES INDICATE GERMAN POSITIONS MARCH 24 AND 26.] The potential strength of the Germans in the western theatre before the Russian revolution was estimated at 4,500,000 rifles, more than half of which were on the front. According to Sir Aukland Geddes, the British Minister of National Service, the secession of Russia added to the enemy's potential strength on the western front possibly as many as 1,600,000 men, of whom 950,000 were Germans. If we add 1,000,000 to the 4,500,000 German rifles in the west we have the 5,500,000 thus produced opposing, at least, 8,500,000 Allies, consisting of French, British, American, Belgian, Portuguese, Russian, and Polish troops. [The British official estimates on April 17 appear on Page 207.]