At 26 or 27 knots, the new ships could dictate an engagement against most torpedo boats. They moved ahead to engage enemy skirmishers and prevent light forces from reaching the capital ships. If an attacker slipped through, the battle fleet's own quick-firing guns supplied another defensive layer. Flotilla defence also required protection for the torpedo craft guarding British bases if enemy torpedo boats attacked them. Destroyers could defeat those attackers while retaining their own torpedo capability. Their 12-pounder guns offered more hitting power than most small opponents required, and the combination with torpedoes made them a threat to cruisers as well.
Chapter · 39:01-41:37
Speed lets early destroyers control the light-force battle
A speed of 26 or 27 knots let the first destroyers control engagements with torpedo boats, clear a path for the battle fleet, and retain a torpedo threat against larger ships.