(2) Commercial Blockade.—To prevent floating commerce from entering or leaving the blockaded harbour. The blockading force would not be powerful enough to prevent a squadron of battleships or cruisers from entering or leaving the port blockaded; and it would not be instituted outside a fortified military port, or one containing a strong naval force. But it would be able to stop scouts and torpedo craft from entering or emerging, unless in very great numbers; and if unable to stop them from emerging, would give warning of their escape and the direction in which they are going.
In both these forms of blockade it is usual, as a matter of courtesy, to allow neutral armed ships belonging to foreign navies to enter and leave for their own purposes, presumably connected with the subjects of their own country who are in the blockaded port. This, however, is not a right, and the country to which the blockading ships belong has a right to refuse it, and to back her refusal by force.
All countries must be notified of a properly instituted commercial blockade, in accordance with International Agreement.
(3) Observing a Port.—This, with its subsidiary operations, should be conducted in such a way as to induce the enemy to put to sea, the object of observing the port being primarily a naval one, viz., to bring him to decisive action.
The principal observing force (consisting of battleships and cruisers) would be either in one squadron, or more, provided that they were in supporting reach of each other, and so placed as to be able to cut off the enemy's fleet on emerging from the port observed before it can get dangerously near its probable objective, and yet sufficiently far out to ensure a battle before it can regain the shelter of its own ports. It is also worth noting that the battle should, if possible, be fought so as to make it difficult for the enemy's damaged ships to obtain the shelter of a friendly neutral's harbours before being captured.
The observed port must be watched closely, so that immediate notice of the enemy's exit may be given; and this would be done by small cruisers, scouts and destroyers, which should be strong and numerous enough to attack any torpedo craft trying to get to sea.
In order to induce the enemy's main force to put to sea it is important that every means be used to prevent his knowing that our fleet is observing the port, or if that be impossible, to do nothing which will lead him to suppose that his port is being observed.
This operation is not a blockade.
Subsidiary operations to induce the enemy's fleet to put to sea, may take the form of a diversion on the enemy's coast, or against some important part of his sea-borne trade, either by the observing fleet or by a force affiliated to it, or by any oversea movements calculated to interfere seriously with the enemy's war plan.