Clearing surface raiders exposed a submarine problem

British surface-war measures appeared to have cleared the principal danger from the trade routes. The Grand Fleet contained the High Seas Fleet, a barrier restricted passage through the Channel, von Spee's squadron had been hunted down, and Goeben and Breslau had been pushed away. By the inherited logic of commerce protection, independent merchant ships could then seem reasonably safe. Submarines introduced a new technology and a different tactical route into the same raiding mission. Convoy policy therefore had to adapt even after the navy had succeeded against the threat it originally expected.