"Use the mortar to sink 3 ships" is an optional mission objective in Sequence 7 / Memory 04: The Fireship
Walkthrough[edit]
As the naval battle starts, call up the Mortar. Aim it ahead toward the incoming ships. Look for the smaller Gunboats or Schooners. Aim for them with the Mortar and loose it upon them. This can severely damage or sink them with relative ease. This is likely to get filled just through fighting as long as you remember to use the mortar.
