A moon pool is a feature of marine drilling platforms, drillship

Drillship

A drillship is a maritime vessel that has been fitted with drilling apparatus. It is most often used for exploratory offshore drilling of new oil or gas wells in deep water or for scientific drilling. The drillship can also be used as a platform to carry out well maintenance or completion work such...

s and diving support vessels

Diving support vessel

A diving support vessel is a ship that is used as a floating base for professional diving projects.Commercial Diving Support Vessels emerged during the 1960s and 1970s when the need arose for diving operations to be performed below and around oil production platforms and associated installations in...

, some marine research

Oceanography

Oceanography , also called oceanology or marine science, is the branch of Earth science that studies the ocean...

 and underwater

Underwater

Underwater is a term describing the realm below the surface of water where the water exists in a natural feature such as an ocean, sea, lake, pond, or river. Three quarters of the planet Earth is covered by water...

 exploration

Exploration

Exploration is the act of searching or traveling around a terrain for the purpose of discovery of resources or information. Exploration occurs in all non-sessile animal species, including humans...

 or research vessels

Watercraft

A watercraft is a vessel or craft designed to move across or through water. The name is derived from the term "craft" which was used to describe all types of water going vessels...

, and underwater habitats, in which it is also known as a wet porch. It is an opening in the floor or base of the hull

Hull (watercraft)

A hull is the watertight body of a ship or boat. Above the hull is the superstructure and/or deckhouse, where present. The line where the hull meets the water surface is called the waterline.The structure of the hull varies depending on the vessel type...

, platform, or chamber giving access to the water below, allowing technician

Technician

A technician is a worker in a field of technology who is proficient in the relevant skills and techniques, with a relatively practical understanding of the theoretical principles. Experienced technicians in a specific tool domain typically have intermediate understanding of theory and expert...

s or researcher

Researcher

A researcher is somebody who performs research, the search for knowledge or in general any systematic investigation to establish facts. Researchers can work in academic, industrial, government, or private institutions.-Examples of research institutions:...

s to lower tool

Tool

A tool is a device that can be used to produce an item or achieve a task, but that is not consumed in the process. Informally the word is also used to describe a procedure or process with a specific purpose. Tools that are used in particular fields or activities may have different designations such...

s and instruments into the sea. It provides shelter and protection so that even if the ship

Ship

Since the end of the age of sail a ship has been any large buoyant marine vessel. Ships are generally distinguished from boats based on size and cargo or passenger capacity. Ships are used on lakes, seas, and rivers for a variety of activities, such as the transport of people or goods, fishing,...

 is in high seas or surrounded by ice, researchers can work in shirt-sleeved comfort rather than on a deck exposed to the elements.