ii. Observation blockade, to force the enemy to put to sea by occupying the common lines of communications (see below). In this case you are seeking a decision as a step towards general control.
Both natures are operations upon the lines of passage and communication, but in case (1) the primary intention is defensive, to secure our own line; in case (2) the primary intention is offensive, to seize the enemy's line and compel him to expose himself in an attempt to recover it.
GENERAL RULES FOR CONDUCTING BLOCKADES
In case (1) (defensive intention) blockade should be as close as is compatible with security from torpedo attack.
In case (2) (offensive intention) it should be as distant
as is compatible with bringing enemy to action if he comes out.
Examples:—Case (1): First stage of Togo's blockade of Port Arthur.
Case (2): Nelson off Toulon.
Confusion of the two: Sampson's attempt to close Santiago simultaneously with an attempt to force Cervera to sea.
THE PECULIARITY OF MARITIME COMMUNICATIONS
Since the whole idea of command of the sea and the whole theory of blockade rest on the control of communications, neither can be fully apprehended without a thorough understanding of the nature of maritime communications.
Ashore, the respective lines of communications of each belligerent tend to run more or less approximately in opposite directions, until they meet in the theatre of operations or the objective point.