Dover Patrol, Harwich Force, and layered Channel defense

The Dover Patrol was only one layer of a wider defensive system. A major German formation entering the Channel risked delay among numerous small targets, attack by local submarines, and interception by heavier forces approaching from more than one direction. British submarines were unlikely to expend torpedoes on small torpedo boats, but cruisers, battlecruisers, and battleships entering the confined area offered worthwhile targets. German late pre-dreadnoughts could also slow a formation that needed speed to force the passage before reinforcements arrived. Harwich Force could approach from the North Sea while the Channel Squadron and other reinforcements gathered beyond the barrage. That geometry made a thrust through the Channel difficult even when individual British patrol units were weak.