able proportion of the distance. Under these conditions, once located by an efficient air scout service, it will be tracked from day to day if need be, and, sooner or later, either by aircraft or destroyer, it will be brought to book. It is not suggested that under no circumstances could a submarine escape, it would, however, only do so by radically altering its course or by some other manoeuvre involving the temporary abandonment of its purpose; ultimately the influence of aircraft on the high seas will be to keep the submarine submerged, under which condition its radius of action is greatly circumscribed. Thus persecuted, it will be reduced to surface running by night, and even then, unless favoured by the elements, will be liable to attack by fast light cruisers or destroyers which will be informed with considerable exactitude as to the whereabouts of their quarry.
Beyond the above, a submarine or submarines tracked by aircraft will have great difficulty in keeping a prearranged rendezvous, and any "neutral" vessel or fishing craft used for fuel supply and revictualling will be far more liable to detection than is at present the case.
The author believes that it is by continuous pressure of this kind, backed up bj'^ direct attack when occasion serves, that submarine activity will eventually be curbed. It has already been pointed out that the capacity of aircraft to warn merchantmen of danger will alone be sufficient to render the submarine threat quite ineffective, apart from any question of destroying the craft themselves.
Such work as contemplated can only be effectively performed by aircraft if sufficiently numerous, operating in units of flights or squadrons. It will be found comparatively useless to endeavour to carry out the duties in question by single machines, since it will often be necessary to sweep considerable areas of the ocean in
186
