How did they supply air to diesel engines on submarines?
First, the diesel engines could not be used submerged without raising the snorkel mast, for those that had snorkel capabilities, or coming to the surface for those without snorkel capabilities. You are correct that they would use a lot of oxygen. Second, if you were under attack you would want to be as deep as possible and the diesel engines would have to exhaust their combustion gases somewhere outside of the boat and at that depth the diesels did not provide enough combustion pressure to overcome sea pressure. Third, and most importantly, THE DIESEL ENGINES MAKE A HELL OF A LOT OF NOISE!!!!!! The best defense a submarine has is its ability to be quiet, especially when operating on its batteries. A running diesel engine would be a signal for the enemy to “drop depth charges here”. If one were under attack and had to start the diesel engines due to the battery running low, odds are the oxygen level would barely be enough to sustain life, much less provide for a diesel engine. There are
