Modern submarine capabilities should not be read backward into 1914. Early boats were closer to submersible torpedo ambushers than to later high-performance submarines, and their underwater speed and weapon supply were limited. HMS Dreadnought even sank a submarine by ramming, a reminder that a surfaced or detected boat could be vulnerable to a large warship. An older cruiser accompanying a slow convoy could force an attacker to rely on scarce torpedoes rather than a deck gun. Concentration and an armed escort reduced the easy opportunities available among scattered merchant ships.
Notable Point · 1:33:20-1:35:10
Why early submarines did not erase the surface escort
First World War submarines were slow submersible ambush craft with limited torpedoes, so armed convoys and surface escorts could still constrain them.