The war manual puts torpedo attack first

The 1920s naval war manual defined destroyers by high speed on a small displacement, torpedoes as the chief weapon, and guns effective against other destroyers. Torpedo attack on enemy ships was the primary tactical function. Additional duties included attacking submarines, destroying disabled ships, and providing tactical security for other fleet units. That security covered threats from torpedo boats, destroyers, and aircraft. Strategic duties could extend to independent operations, sea control, and minesweeping. The manual therefore combined a clear weapon priority with a broad set of fleet and independent responsibilities.