Port-holes were used for:

Port-holes, also known as portholes, were an important feature of ships and submarines. They served several purposes and were integral to the functioning and safety of these vessels. Here are the details:

1. Providing Light and Ventilation:
- Port-holes were primarily designed to allow natural light to enter the ship's interior spaces.
- They were strategically placed in the ship's hull to ensure that light could reach even the deepest parts of the vessel.
- In addition to light, port-holes also allowed fresh air to circulate inside the ship, improving ventilation and preventing stale air from accumulating.

2. Enhancing Visibility:
- Port-holes were made of glass and provided a means for the crew to see outside the ship.
- They offered a limited view of the surrounding environment, allowing the crew to monitor the conditions outside.
- This was particularly important for submarines, as they needed to surface periodically to recharge their batteries and assess the situation above water.

3. Emergency Escape Routes:
- In times of emergency, port-holes could be used as escape routes.
- They were large enough for crew members to fit through and provide an alternative means of evacuation if other exits were blocked or inaccessible.
- However, escaping through a port-hole could be dangerous, especially during combat situations or adverse weather conditions.

4. Defense and Protection:
- Port-holes could be closed and sealed to protect the ship from water ingress during rough weather or combat.
- They were equipped with sturdy covers or shutters that could be secured to prevent water from entering the ship.
- This helped to keep the interior spaces dry and prevent damage to sensitive equipment or cargo.

5. Aesthetic and Symbolic Purposes:
- Port-holes also served an aesthetic function, adding visual interest to the ship's exterior.
- They were often arranged in symmetrical patterns along the ship's sides, contributing to its overall design and appearance.
- In addition, port-holes symbolized the maritime heritage and were a recognizable feature of seafaring vessels.

In conclusion, port-holes played a crucial role in ships and submarines, providing light, ventilation, visibility, emergency escape routes, defense, and adding to the vessel's aesthetic appeal.