The Pirate Cap is a special manually-controlled tower that appears in Buccaneer's Den. He operates a cannon battery that fires one or several shots that hit enemies in a small area.
Hire pirates cannons and blast enemies.
The Pirate Cap is the owner of the smaller ship to the left. For a small sum of money, he can be paid to fire the cannonade battery on the starboard side of his ship:
A second after that, the cannons will fire on the selected spot, dealing 60-120 damage per shot to enemies in a small area. There's no cooldown.
The Cannonade can be used in a similar manner to Rain of Fire, with the limitation being money rather than the cooldown. Its shots can be very efficient against dense groups of enemies or to catch lone leaking enemies, but not so much against tough enemies like Executioners.
As with Rain of Fire, there is a slight delay between you choosing the spot and the damage being done. As such, be sure to target just ahead of moving enemies to ensure they are fully in range of the damage being done.