Blackout (wartime)

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Blackout (wartime)

A blackout in time of war

War

...
, or apprehended war, refers to the practice of collectively minimizing external light

Light

Light, or visible light, is electromagnetic radiation of a wavelength that is Visible spectrum to the human eye , or up to 380?750 nm. In the broader field of physics, light is sometimes used to refer to electromagnetic radiation of all wavelengths, whether visible or not....
, including upward-directed (or reflected

Reflection (physics)

Reflection is the change in direction of a wavefront at an wiktionary:interface between two differentmedium so that the wavefront returns into the medium from which it originated....
) light. This was done in the 20th century to keep the crews of enemy aircraft from being able to navigate

Navigation

Navigation is the process of reading, and controlling the movement of a craft or vehicle from one place to another. It is also the term of art used for the specialized knowledge used by navigators to perform navigation tasks....
to their targets simply by sight.

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A blackout in time of war

War

...
, or apprehended war, refers to the practice of collectively minimizing external light

Light

Reflection (physics)

Navigation

Ship

A ship is a large watercraft that floats on water. Ships are generally distinguished from boats based on size. Ships may be found on lakes, seas, and rivers and they allow for a variety of activities, such as the ferry or cargo ships, fishing, cruise ship, Coast guard, and warship....
s from being seen in silhouette

Silhouette

A silhouette is a view of an object or scene consisting of the outline and a featureless interior, with the silhouetted object usually being black....
against the shore and attacked by enemy submarine

Submarine

A submarine is a watercraft capable of independent operation below water. It differs from a submersible, which has only limited underwater capability....
s farther out at sea.

Lights can simply be turned off or light can sometimes be minimized by tar

Tar

Tar is modified resin produced from the wood and roots of pine by destructive distillation under pyrolysis. It is a viscosity black liquid. Production and trade in tar was a major contributor in the economies of Northern Europe and Colonial America....
ring the windows of large public structures.

These benefits against air attack are now largely nullified in the face of a technologically sophisticated enemy. As early as World War II

World War II

World War II, or the Second World War , was a global military conflict which involved a Participants in World War II, including all of the great powers, organised into two opposing military alliances: the Allies of World War II and the Axis powers....
, aircraft were using radio

Radio

Radio is the transmission of signals, by modulation of electromagnetic radiation with frequency below those of visible light.Electromagnetic radiation radio propagation by means of oscillating electromagnetic fields that pass through the air and the vacuum of space....
-beam navigation (see battle of the beams

Battle of the beams

The Battle of the Beams refers to a period in early World War II when bombers of the German Air Force started using radio navigation for night bombing....
), and targets were detected by air-to-ground radar

Radar

Radar is a system that uses electromagnetic radiation waves to identify the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, ships, motor vehicles, weather formations, and terrain....
, (e.g. H2X

H2X radar

The H2X radar, nicknamed the "Mickey set", provided the United States Army Air Forces with ground mapping capability during daylight overcast and nighttime operations in World War II....
). Today, not only are night vision goggles

Night vision goggles

A night vision device is an optical instrument that allows images to be produced in levels of light approaching total darkness. They are most often used by the military and police agencies, but are available to civilian users....
readily available to air crews, but sophisticated satellite

Satellite

In the context of spaceflight, a satellite is an Physical body which has been placed into orbit by human endeavor. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
-based and inertial navigation systems enable a static target to be found easily by either an aircraft or a guided missile

Guided Missile

Guided Missile is a London based independent record label set up by Paul Kearney in 1994 in music.Guided Missile has always focused on 'the underground', preferring to put out a steady flow of considered and quality releases and developing the numerous and now essential GM...
.

During the Battle of the Atlantic

Second Battle of the Atlantic

The Battle of the Atlantic was the longest continuous military campaignof World War II,running from 1939 through the defeat of Nazism Nazi Germany in 1945, and was at its height from mid-1940 through to the end of 1943....
in World War II

World War II

U-boat

U-boat is the anglicized#Loanwords version of the German language word , itself an abbreviation of Unterseeboot , and refers to military submarines operated by Germany, particularly in World War I and World War II....
s were greatly aided in the "second happy time

Second happy time

The Second Happy Time was the informal name for a phase in the Second Battle of the Atlantic during which Axis Powers submarines attacked merchant shipping along the east coast of North America....
" with the sinking of unescorted ships in American coastal waters, because the ships were back lit by coastal lights. In any naval war, this would still be an advantage which a blackout would help to nullify.