What is an access hatch in a submarine?

On modern submarines, there are typically 4 primary access hatches - 1 in the bow, 1 in the stern, one on the bridge (at the top of the sail, or fairwater), and one hatch amidships. On most Submarines the center hatch (and most frequently used in port) is called the Weapons Shipping Hatch. This is because it is the only hatch which is at a 45 degree angle, as its primary function is for loading torpedoes and other weapons into the Torpedo Room.

The fore and aft access hatches on U.S. boats are also entrance and exits for the 2 Escape Trunks, used for crew escape, or for certain configured boats, SEAL delivery. All hatches have an inner and outer hatch to further ensure the inner pressure hull is not comprimised should an outer hatch seal fail for any reason.

Hatches also have a safety latch mechanism, that is to keep the hatch from being blown open by pressure in the boat when the hatch is opened after the boat has been submerged for some time. Such pressure can literally eject the opening crewman out of the hatchway. The latch provides a slower release, as well as a safety mechanism to keep the crewmember safe.