Bar armor

Bar armor was a way of providing protection from RPGs (Rocket Propelled Grenades) without making the vessel too heavy to float. Made from concrete reinforcing bars or "re-bars", their purpose was to explode the rocket before it hit the hull or the superstructure, thereby reducing the thickess of plating needed to stop the schrapnel. The bars were welded a few inches apart in a grillwork and were spaced about 18" away from the hull. The space between the bars and the hull was filled with styrafoam for a little extra flotation. Above the waterline, the space was often used for boxes of C-rations and other storage.

In actuality, the bars did work most of the time, but not always. A lucky shot could get through to impact the plating below and blow a hole the size of your fist through it, spraying hot metal around inside. I'm grateful for the times that the bars saved my butt.