[AO1_AW_SW_USN]

Two reasons:

1. Turning off unnecessary lights helps conserve the precious energy stored in the battery.

2. Turning off/on the lights is a much better way to communicate to a submariner to secure for silent running, rather than using a very noisy interior communication announcement system between compartments.


In addition, it is believed by some that play this game that the bright white lights are switched to red to indicate the time of sunset. This is partially true.

Bright lights are switched to red at sunset to all hatches and watertight doors leading to weather decks (outside access to a ship or vessel). This is because red lights are much more difficult to spot at night rather then a bright white light, thus making the ship of vessel difficult to spot by unfriendly units. This is called "Darken Ship" in most of the world's Navies and it's practiced by all, even in peacetime.