Exercise OD rehearsed convoy interception and night battle

OD gave a weaker but faster force the task of attacking a protected convoy while avoiding the enemy's superior battle strength. The scenario placed bases at Malta and Port Said and made Derna an advanced base under siege by red land forces. Blue submarine attacks on red communications had left the besieging army urgently short of reinforcements and stores, so the convoy's passage had a direct effect ashore. Ships represented absent battlecruisers and other units, allowing the exercise to model a larger operational force than the fleet physically available. The open-ended format let the commander-in-chief continue the problem until the participants had extracted its useful lessons. The commander-in-chief controlled Red but allowed Blue's plan to continue instead of ending the contest at a convenient point for his own side.