Blockade demands naturally a certain division of forces, and the battle-fleet of the attacking party, which is supposed to lie behind the farthest lines of blockade and observation, cannot always hold the high seas in full strength.

The forces of the defending party, however, lie in safe anchorages, ready to sally out and fight.
Such a blockade might, after all, be very costly to the attacking party.
We may therefore fairly assume that the English would decide in favour of the second kind.

At all events, the harbour constructions, partly building, partly projected, at Rosyth and Scapa Flow, were chosen with an eye to this line of blockade.

It would entail in the north the barring of a line about 300 nautical miles long, a scheme quite feasible from the military aspect.

Only a small force is required to seal up the Channel, as the navigation route is very narrow.