An invasion of Great Britain must always be an attempt over an uncommanded sea. It may be that our fleet predominates or it may be that it does not, but the command must always be in dispute. If we have gained complete command, no invasion can take place, nor will it be attempted. If we have lost it completely no invasion will be necessary, since, quite apart from the threat of invasion, we must make peace on the best terms we can get. Now, if the sea be uncommanded, there are obviously two ways in which an invasion may be attempted. Firstly, the enemy may endeavour to force it through our naval defence with transports and fleet in one mass. This was the primitive idea on which the Spanish invasion of Philip the Second was originally planned by his famous admiral, Santa-Cruz. Ripening military science, however, was able to convince him of its weakness. A mass of transports and warships is the most cumbrous and vulnerable engine of war ever known. The weaker the naval defence of the threatened country, the more devoutly will it pray the invader may use this device. Where contact with the enemy's fleet is certain, and particularly in narrow seas, as it was in this case, such a course will give the defender all the chances he could desire, and success for the invader is inconceivable, provided always we resolutely determine to make the army in its transports our main objective, and are not to be induced to break our head against its escort. Where, however, contact is not certain, the invasion over an uncommanded sea may succeed by evasion of the defender's battle-fleet, as it did in the case of Napoleon's invasion of Egypt. But that operation belongs to an entirely different category from that which we are now considering. None of the factors on which the traditional system of British defence is based were present. It was an operation over an open sea against a distant and undetermined objective that had no naval defence of its own, whereas in our own case the determining factors are permanent naval defence, an approximately determined objective, and a narrow sea where evasion by any force of invasion strength is impossible. Napoleon's exploit was in fact nothing more than the evasion of an open blockade which had no naval defence beyond it. The vital importance of these things will appear as we proceed and note the characteristics which marked every attempt to invade England. From such attempts we of course exclude the various descents upon Ireland, which, not being of invasion strength, fall into another class, to be dealt with hereafter.