As opposed to this was the openness of England, France, and Russia to naval attack. England has but a small proportion of land to seacoast, and France is open to the sea on three sides. Russia, fronting the Baltic, possessed an infinitely inferior fleet, to which the Allies could send no reenforcement as long as the Skagerrak and Cattegat Straits were the only way into the Baltic; moreover, by the Kiel Canal, connecting the North Sea and the Baltic, the remodeling of which was completed in a few months before the declarations of war, a German naval fleet would possess an enormous advantage over an allied fleet, endeavoring to force entrance into the Baltic. In addition to this, while the Central Powers could work together on both fronts with great ease, thanks to the excellent system of German railways, Great Britain and France had no means of direct communication with their great ally in the east of Europe. Thus, in a measure, the Central Powers were not attacking the Allies at any one time, though it might truly be said that they were being attacked by the Allies. In the event of any lack of synchronization between the plans of Russia and those of the western allies, German and Austrian troops could be massed first on one side of the field of operations and then on the other. Such action was impossible to the Allies. At the time of the great German advance on Paris, Russia could give no aid. At the time of the German advance on Riga, Britain and France could give no aid. Both German advances were checked and the invaders driven back, not by the armies of the Allies, but by two non-interlocking parts of the armies of the Allies. At the same time, the susceptibility to attack on both sides prevented the Central Powers from deflecting all their men to either front, and thus by the mere existence of passive menace, prevented the Central Powers from using their geographic advantage to the full. Their disadvantage, in the military sense of the recognition of geographical conditions, was that the Central Powers had constantly to bear in mind the necessity of fighting upon two fronts. Russian activity, while important to Britain and France, was a matter with which their policy had nothing to do; the coordination of movements on the west front was a matter entirely outside the scope of the operations of the Russian commanders. The German military staff, on the other hand, had the task of constantly coordinating two separate campaigns, to determine where the greatest number of men should be, to avoid weakening the one side or the other at the wrong moment.