Commerce destruction does not break the blockade

The distinction is between denial and control. Submarines might make British use of the sea more costly, but they could not escort German merchant shipping or reopen imports. Contemporary U-boats were largely submersible torpedo boats with limited underwater endurance, and Britain could eventually organize broader convoy protection. Germany's central strategic need was to break the blockade and recover access to overseas goods; unrestricted submarine warfare did not achieve that task in this period. Sinking commerce and restoring one's own maritime access are strategically different accomplishments.