Targets, targets, and MORE targets.
Lightly defended targets of opportunity.
Consider the sea going barges and troop carriers used in the Pacific as a start.
Carried troops, supply's, perhaps a tank, etc.
Tramp steamers chugging along at 8knots from port to port with a mixed cargo.
In short, more things to kill.
Also it ties into special events as noted, and immersion as well.