City Destroyers are enormous spacecrafts that were used by the Harvesters as their main attack force during the War of 1996 and they are featured in the 1996 sci-fi movie Independence Day.
A City Destroyer is, by Earth standards, of staggering size: shaped overall like a concave saucer, its diameter is of 15 miles (or 25 kilometers) and its height from the center up is of just under four kilometers, tapering out to a single kilometer on the brim. The brim is not perpendicular to the bottom of the ship; instead, the edge of the bottom expands outward slightly before uniting with the upper dome. The upper dome is not perfectly smooth: the control tower, a wafer-shaped structure longer and taller than it is wide (though not so tall as to be the ship's tallest point), protrudes from a dish-shaped indentation near the edge roughly three or four kilometers in diameter. The underside of the ship is not uniform either: it is arranged in a symmetrical, bas-relief design not unlike the petals of a flower, with street-like corridors separating warehouse-sized blocks.
Purpose and Operation
City Destroyers are deployed more or less simultaneously from the Mothership in order to hover over strategic locations on the target planet. As soon as the ships are deployed, a countdown begins. Once all the Destroyers are in position and the countdown reaches zero, the first volley of the firing procedure begins - that is, all the Destroyers open the ports at the center of their underside which houses their main weapon: a devastating cannon/mining laser. Once the weapon is charged, the Destroyers simultaneously launch a ball of energy that disintegrates its target and then expands out with destructive force sufficient to demolish an area the size of a large city. If more targets must be hit in order to obtain control of the planet, another countdown then presumably begins as the ships re-position to destroy targets unaffected by the first volley.
In case of counterattack by the residents of the besieged planet (as well as to destroy smaller targets impractical for the Destroyers to attack), the Destroyers will deploy Attackers, which are small, nimble crafts designed for dogfighting. This pattern continues for any additional volleys. The volleys are also potent enough to level an entire mountain, which is best demonstrated on how a City Destroyer managed to completely obliterate NORAD at Mt. Cheyenne. Like the attackers, they also carried powerful deflector shields, being capable of withstanding up to a nuclear warhead without so much as a scratch. This was best demonstrated during the failed nuclear strike on a City Destroyer above Houston, which destroyed the city but the City Destroyer remained completely unaffected.
The ships have weaknesses, however: they are just as susceptible to computer viruses when infected (although they have a slight delay in being infected). In addition, the use of their onboard cannon also carries the risk of being destroyed by a missile/suicide attack while charging up a volley, which would result in catastrophic damage to the ship. This was ultimately how the City Destroyer targeting Area 51 and all of the other City Destroyers during the War of 1996 were taken down.
In the War of 1996, thirty-six City Destroyers participated in the invasion of Earth and destroyed at least 108 human cities. The City Destroyers were finally brought down during the July 4th counterattack after the Americans managed to disable their shields and discovering their weakness in their exposed primary weapons. After the war, the destroyed vessels were mined by humanity for their resources and technology.
Although the City Destroyers were taken down, one intact Destroyer managed to land in the African nation of Umbutu. This vessel drilled into the Earth until it was deactivated when the mothership was destroyed during the July 4th counterattack. However, the aliens of the vessel kept fighting Umbutu's military forces for 10 years until they were eradicated. The Destroyer remained dormant and Umbutu's isolationist policies prevented the international world from investigating the vessel.
In 2016, the Umbutu Destroyer was suddenly reactivated. This forced Umbutu's leader Dikembe Umbutu to request the aid of ESD Director David Levinson to investigate the vessel. It was then learned that the Destroyer had sent a distress call to its home planet, sending the Harvester Mothership with the Harvester Queen to Earth.