Do submarines leak?

It may be a bit unnerving to learn that submarines do leak and that it is intentional. Some parts of the boat that need to extend through the hull may need to move. These include the propellors, the bow and stern planes and the periscopes. It is possible to tighten the packing around these structures so that the leak is stopped entirely. Unfortunately, the devices would have been stopped as well; they would no longer rotate. The small amount of water that is leaking into the boat also acts as a lubricant.

The rate of the leak is normally not a concern. It is easy to pump the water out periodically.