A well deck or well dock is a hangar-like deck

Deck (ship)

A deck is a permanent covering over a compartment or a hull of a ship. On a boat or ship, the primary deck is the horizontal structure which forms the 'roof' for the hull, which both strengthens the hull and serves as the primary working surface...

 located at the waterline

Waterline

The term "waterline" generally refers to the line where the hull of a ship meets the water surface. It is also the name of a special marking, also known as the national Load Line or Plimsoll Line, to be positioned amidships, that indicates the draft of the ship and the legal limit to which a ship...

 in the stern of some amphibious warfare ship

Amphibious warfare ship

Amphibious warfare ship, often shortened to amphibs or phibs and popularly known as gator freighters, denotes a range of classes of warship employed to land and support ground forces, such as marines, on enemy territory during an amphibious assault...

s. By taking on water the ship can lower its stern, flooding the well deck and allowing boats and amphibious landing craft to dock within the ship. This facilitates moving cargo between the ship and smaller craft during amphibious operations

Amphibious warfare

Amphibious warfare is the use of naval firepower, logistics and strategy to project military power ashore. In previous eras it stood as the primary method of delivering troops to non-contiguous enemy-held terrain...

. Well decks are a feature of modern types of amphibious warfare ship such as the amphibious transport dock

Amphibious transport dock

An amphibious transport dock, also called a landing platform/dock , is an amphibious warfare ship, a warship that embarks, transports, and lands elements of a landing force for expeditionary warfare missions. Several navies currently operate this kind of ship...

, dock landing ship

Dock landing ship

A Dock landing ship or Landing ship is a form of amphibious warship designed to support amphibious operations. These amphibious assault ships transport and launch amphibious craft and vehicles with their crews and embarked personnel...

 and Landing Helicopter Dock.