The initial blockade group consists of one battlecruiser and a dozen destroyers facing a German battleship and destroyer near the contested port. That balance is too risky for the battlecruiser despite its numerous escorts. Adding a battleship creates a combined group strong enough to discourage the German capital ship from sortieing. A credible blockade requires enough concentrated combat power to defeat an attempted breakout.
Notable Point · 1:08:37-1:10:06
Capital-ship cover makes a blockade force credible
A battleship joins a battlecruiser and destroyer group so an enemy battleship cannot break the local blockade on favourable terms.