Saltwater is very corrosive. You have to strip paint and treat the metal underneath to stop the corrosion, as the slightest crack or pore in the paint allows c

Saltwater is very corrosive. You have to strip paint and treat the metal underneath to stop the corrosion, as the slightest crack or pore in the paint allows corrosion to start unseen. The only way to fully waterproof the inside of a submarine is to keep the water outside.