Today’s invention is a way to provide surface ships with additional protection against incoming ballistics (such as heavy machinegun fire or rocket-propelled grenades from pirate ships).
It’s well known that high energy projectiles destroy themselves on penetrating a relatively small depth of water.
The idea is therefore to attach to surface ships a number of modular, tanks. These would normally be air filled and travel around the waterline, providing some extra stability in choppy weather.
When under attack, the tanks would be dropped into the sea, allowed to fill with water and then hoisted into position as shown. This would provide an effective, shell-proof barrier around the deck, lower the vessel’s profile and allow vital extra time to call in support.