Depth charges are anti-Submarine explosive weapons that are exclusive to the Destroyer.
It can be built by placing down one Obsidian block on a Destroyer, under y 66. The Obsidian must be touching water outside the ship in order for it to launch.
Place down a sign on the Obsidian block and type DepthCharge on the first line.
After right clicking on the sign, the Depth Charge is launched downwards. It will detonate in the water and deal damage to all Submarines in a 120 block radius around it.