For any of these reasons we may decide that the best way of realising our object is to use close blockade, but the matter does not end there. We have still to consider whether close blockade is within the limit of the force we have available, and whether it is the best method of developing the fullest potentialities of that force. Close blockade being the more exhausting form will require the greater strength; we cannot blockade closely for any length of time without a force relatively superior; but if by open blockade of a squadron we permit it to put to sea with contact assured, we know that, even with a slightly inferior force, we can so deal with it as to prevent its getting local control sufficient to break down our mobile flotilla defence or to interfere seriously with our trade. Finally, there is the question of risk. In the old days, before free movement and wireless telegraphy, and before the flotilla had acquired battle power, there was always to be faced the risk of not getting contact in time to prevent mischief. This consideration was specially dominant where the enemy had a squadron within or near the critical theatre of operations. Therefore when the invasion threatened, our developed policy was to blockade Brest closely at almost any sacrifice. There was always a vague possibility that by evasion or chance of wind a squadron so close to the line of invasion might get sufficient temporary command in the vital area before it could be brought to action. It was a possibility that was never realised in the Narrow Seas, and since mobility of fleets and means of distant communication have so greatly increased in range and certainty, and since the power of resistance in the flotilla has become so high, the risk is probably much less than ever, and the field for open blockade is consequently less restricted.