Blackout (wartime)
A blackout during war
War is a state of organized, armed, and often prolonged conflict carried on between states, nations, or other parties typified by extreme aggression, social disruption, and usually high mortality. War should be understood as an actual, intentional and widespread armed conflict between political...

, or apprehended war, is the practice of collectively minimizing outdoor light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...

, including upwardly directed (or reflected
Reflection (physics)
Reflection is the change in direction of a wavefront at an interface between two differentmedia so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves...

) light. This was done in the 20th century to prevent crews of enemy aircraft from being able to navigate
Navigation is the process of monitoring 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, for example during the London Blitz of 1940. In coastal regions, a shore-side blackout of city lights would also help protect 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,...

s from being seen in silhouette
A silhouette is the image of a person, an object or scene consisting of the outline and a basically featureless interior, with the silhouetted object usually being black. Although the art form has been popular since the mid-18th century, the term “silhouette” was seldom used until the early decades...

 against the shore and attacked by enemy submarine
A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...

s farther out at sea.

Lights can simply be turned off or light can sometimes be minimized by tar
Tar is modified pitch produced primarily from the wood and roots of pine by destructive distillation under pyrolysis. Production and trade in tar was a major contributor in the economies of Northern Europe and Colonial America. Its main use was in preserving wooden vessels against rot. The largest...

ring the windows of large public structures. In World War II, a dark blackout curtain
A curtain is a piece of cloth intended to block or obscure light, or drafts, or water in the case of a shower curtain. Curtains hung over a doorway are known as portières...

 was used to keep the light inside. Tarring the windows can mean a semi-permanent blackout status; Grand Central Terminal
Grand Central Terminal
Grand Central Terminal —often incorrectly called Grand Central Station, or shortened to simply Grand Central—is a terminal station at 42nd Street and Park Avenue in Midtown Manhattan in New York City, United States...

's World War II blackout paint was not fully removed from its windows until 2009.

World War II

The British experience serves as an example of enforced blackout.

The Air Ministry
Air Ministry
The Air Ministry was a department of the British Government with the responsibility of managing the affairs of the Royal Air Force, that existed from 1918 to 1964...

 had forecast that Britain would suffer night air bombing attacks causing large numbers of civilian casualties and mass destruction. It was widely agreed that navigation and targeting would be more difficult if man-made lights on the ground could be extinguished. As early as July 1939, Public Information Leaflet No 2 (part of the Air Raid Patrol
Air Raid Precautions
Air Raid Precautions was an organisation in the United Kingdom set up as an aid in the prelude to the Second World War dedicated to the protection of civilians from the danger of air-raids. It was created in 1924 as a response to the fears about the growing threat from the development of bomber...

 (A.R.P.) training literature) warned of the need for popular discipline to ensure that the blackout regulations were fully enforced during the blackout periods.

Blackout regulations were imposed on 1 September 1939, before the declaration of war. These required that all windows and doors should be covered at night with suitable material such as heavy curtains, cardboard or paint, to prevent the escape of any glimmer of light that might aid enemy aircraft. The Government ensured that the necessary materials were available. External lights such as street lights were switched off, or dimmed and shielded to deflect light downward. Essential lights such as traffic lights and vehicle headlights were fitted with slotted covers to deflect their beams downwards to the ground.

Shops and factories had particular problems. Factories with large areas of glass roofing found it impossible to install temporary blackout panels and permament methods (such as paint) lost natural light during daylight. Shops had to install double "airlock" doors to avoid lights showing as customers arrived and departed.

The blackout was enforced by civilian ARP wardens who would ensure that no buildings allowed the slightest chink or glow of light. Offenders were liable to stringent legal penalties.

Blackout restrictions greatly increased the dangers of night driving and fatalities increased as a consequence. As a result, some aspects were relaxed and speed limits were lowered. The anticipated increase in crime rates did not occur.

German war-making capability declined and a "Dim-out" was introduced in September 1944, which allowed lighting to the equivalent of moonlight to be introduced. A full Blackout would be imposed if an alert was sounded. Full street lighting of streets was allowed in April 1945, on 30 April, Big Ben was lit after 5 years and 123 days of the Blackout descended.

The United States was not exposed to air attack, but along the Atlantic coast, the lack of a coastal blackout served to silhouette Allied shipping and thus expose them to German submarine attack. Coastal communities resisted the imposition of a blackout for amenity reasons, citing potential damage to tourism. The result was a disastrous loss of shipping, dubbed by German submariners as the "Second Happy Time
Second happy time
The Second Happy Time , also known among German submarine commanders as the "American shooting season" was the informal name for a phase in the Second Battle of the Atlantic during which Axis submarines attacked merchant shipping along the east coast of North America...


Modern technology

The benefits of blackouts 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 conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

, aircraft were using radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels 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 was a period early in the Second World War when bombers of the German Air Force used a number of increasingly accurate systems of radio navigation for night bombing. British "scientific intelligence" at the Air Ministry fought back with a variety of increasingly effective...

"), and targets were detected by air-to-ground radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...

, (e.g. H2X
H2X radar
H2X radar was an American development of the British H2S radar, the first ground mapping radar to be used in combat. It was used by the USAAF during World War II as a navigation system for daylight overcast and nighttime operations...

). Today, not only are night-vision goggles readily available to air crews, but sophisticated satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. 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 aircraft and guided missile
Guided Missile
Guided Missile is a London based independent record label set up by Paul Kearney in 1994.Guided Missile has always focused on 'the underground', preferring to put out a steady flow of releases and developing the numerous GM events around London and beyond....

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