[5] Wellington’s view of the essential factor was expressed to Rear Admiral Martin, who was sent to Spain by the Admiralty to confer with him in September 1813.  “If anyone,” he said, “wishes to know the history of this war, I will tell them it is our maritime superiority gives me the power of maintaining my army while the enemy are unable to do so.” (Letters of Sir T. Byam Martin) [Navy Records Society], ii, p. 499.

But what if the conditions of the struggle in which we wish to intervene are such that no truly limited theatre is available?  In that case we have to choose between placing a contingent frankly at the disposal of our ally, or confining ourselves to coastal diversion, as we did at Frederick the Great’s request in the early campaigns of the Seven Years’ War.  Such operations can seldom be satisfactory to either party.  The small positive results of our efforts to intervene in this way have indeed done more than anything to discredit this form of war, and to brand it as unworthy of a first-class Power.  Yet the fact remains that all the great continental masters of war have feared or valued British intervention of this character even in the most unfavourable conditions.  It was because they looked for its effects rather in the threat than in the performance.  They did not reckon for positive results at all.  So long as such intervention took an amphibious form they knew its disturbing effect upon a European situation was always out of all proportion to the intrinsic strength employed or the positive results it could give.  Its operative action was that it threatened positive results unless it were strongly met.  Its effect, in short, was negative.  Its value lay in its power of containing force greater than its own.  That is all that can be claimed for it, but it may be all that is required.  It is not the most drastic method of intervention, but it has proved itself the most drastic for a Power whose forces are not adapted for the higher method.  Frederick the Great was the first great soldier to recognise it, and Napoleon was the last.  For years he shut his eyes to it, laughed at it, covered it with a contempt that grew ever more irritable.  In 1805 he called Craig’s expedition a “pygmy combination,” yet the preparation of another combined force for an entirely different destination caused him to see the first as an advance guard of a movement he could not ignore, and he sacrificed his fleet in an impotent effort to deal with it.

It was not, however, till four years later that he was forced to place on record his recognition of the principle.  Then, curiously enough, he was convinced by an expedition which we have come to regard as above all others condemnatory of amphibious operations against the Continent.  The Walcheren expedition is now usually held as the leading case of fatuous war administration.  Historians can find no words too bad for it.  They ignore the fact that it was a step—­the