The first step towards obtaining "command of the sea" is the removal of the obstacles which stand in one's way. In this particular case the main obstacle (admittedly constructed for the purpose) was the German High Seas Fleet. Thus the first duty of the British Grand Fleet was that of destroying the {4} so-called High Seas Fleet, or, if destruction was found to be impracticable, of reducing it to inactivity. The German Fleet was fully alive to that fact, and, almost throughout the war, hid themselves away in their naval bases under the protection of their coast defences. Thus, as events showed, the High Seas Fleet did not prove to be a very serious obstacle to our Command of the sea; but, and this fact is easily forgotten, we could not _foresee_ the continuance of their ineptitude and lack of spirit. The German submarines, however, were a formidable obstacle, indeed. It is unnecessary to reiterate what is already common knowledge on that point. Submarines, by their nature, have certain limitations. Except in the case of the submarine cruisers, which only materialised in the latter part of the war, such craft are considerably hampered in their movements by their comparatively small radius of action. Owing to the geographical situation of Germany, her submarines were forced to expend an important percentage of their fuel during the outward and homeward voyages between their bases and the trade routes. This expenditure cannot merely be judged by the distances which had to be traversed; the expenditure of fuel in the submarine bears some relation to the _whole circumstances_ of the voyage. The endurance of the personnel is another important factor, and is similarly affected by the circumstances under which they are employed. For instance, in waters patrolled by enemy vessels, high speed must always be readily available and the strain on the personnel, consequent on the danger of sudden attack from surface craft, aircraft, or other submarines, {5} to say nothing of the presence of mine-fields, is increased. Thus the longer the passage that the German submarines were forced to undertake in comparatively narrow and dangerous waters--such as the North Sea--the less work could they do on our more important trade routes. That statement is closely connected with the subject of this book. It did not require very much intelligence on the part of the German Admiralty to realise that the possession of bases on the Flanders coast would greatly facilitate their submarine campaign owing to the consequent reduction of the voyages to and from the trans-Atlantic, or Channel, trade routes. Flanders was therefore used, as will be explained later in detail, to provide advanced bases for German submarines.