The comment frames close blockade as a two-sided removal of combat power. The enemy is contained in port, but the blockader also commits a large squadron and a significant part of its fleet train. Constant station-keeping wears down the ships outside while the sheltered force avoids the same material erosion. Radio direction finding could also expose talkative support traffic, giving a fast cruiser opportunities to raid the logistics on which the blockade depends.
Notable Point · 24:13-24:50
The hidden cost of maintaining a close blockade
A close blockade consumes ships and fleet-train capacity while steadily wearing down the blockading force more than the force sheltered inside port.