Complex sentence: If a larger Italian force attacked the convoy, Vian was to protect the convoy with smoke and the escorts were to repulse the attackers with torpedoes and try to inflict early casualties using gunfire against two of the Italian ships.
Split into simpler sentences: If a larger Italian force attacked the convoy, Vian was to protect the convoy with smoke. The escorts were to repulse the attackers with torpedoes and to inflict early casualties with gunfire on two selected Italian ships.