So far as can be seen there is no present likelihood of the transport of food or raw materials being effected in anything but vessels which move upon the surface of the sea.

It is true that, as a result of the war, people's thoughts turn in the direction of transport, both of human beings and of merchandise, by air or under the water, but there is no possible chance, for at least a generation to come, of either of these methods of transport being able to compete commercially with transport in vessels sailing on the sea.

Therefore the problem of guarding our communications resolves itself into one of securing the safety of vessels which move upon the surface of the sea, whatever may be the character of the attack.
I do not desire to enter into any discussion here as to the method by which these vessels can be protected, except to say that it is necessary for us to be in a position of superiority in all the weapons by which their safety may be endangered.

At the present time there are two principal forms of attack: (1) by vessels which move on the surface, and (2) by vessels which move under water.

A third danger--namely, one from the air--is also becoming of increasing importance.