Final answer:
The Convoy Battle Drills refer to strategies combining direct and indirect methods of attack, with the convoy system during WWI being an example of an indirect method. Flanking is a maneuver that involves a side attack rather than a direct frontal assault.
Step-by-step explanation:
The types of Convoy Battle Drills are not specified in traditional terms, but they are tactics developed based on the combination of direct and indirect methods of attack. In the context of World War I, the convoy system was a military tactic employed to counter the threat of German U-boats.
One such maneuver that involves attacking indirectly is called flanking, which consists of moving around the side of an army rather than engaging directly from the front. This is an example of an indirect attack that complements the convoy system's strategic defense.