Operations at Groom Lake :
Groom Lake is not a conventional airbase, and front-line units are not normally deployed there. It appears, rather, to be used during the development, test and training phases for new aircraft. Once those aircraft have been accepted by the USAF, operation of that aircraft is generally shifted to a normal airforce base. Groom is reported, however, to be the permanent home for a small number of aircraft of Soviet design (obtained by various means). These are reportedly analysed and used for training purposes.
Soviet spy satellites obtained photographs of the Groom Lake area during the height of the Cold War, but these support only modest conclusions about the base. They depict a nondescript base, airstrip, hangars, etc., but nothing that supports some of the wilder claims about underground facilities. Later commercial satellite images show the base has grown, but remains superficially unexceptional.
Senior Trend / U-2 program :
Groom Lake was used for bombing and artillery practice during World War II, but was then abandoned until 1955, when it was selected by Lockheed's skunkworks team as the ideal location to test the forthcoming U-2 spyplane. The lakebed made for an ideal strip to operate the troublesome test aircraft from, and the Emigrant Valley's mountain ranges and the NTS perimeter protected the secret plane from curious eyes.
Lockheed constructed a makeshift base at Groom, little more than a few shelters and workshops and a small constellation of trailerhomes to billet its small team in. The first U-2 flew at Groom in August of 1955, and U-2s under the control of the CIA began overflights of Soviet territory by mid-1956.
During this period, the NTS continued to perform series of atmospheric nuclear explosions. U-2 operations throughout 1957 were frequently disrupted by the Plumbbob series of atomic test, which exploded two dozen devices at the NTS. The Plumbbob-Hood explosion scattered fallout across Groom and forced its (temporary) evacuation.
As U-2's primary mission was to overfly the Soviet Union, it operated largely from airbases near the Soviet border, including Incirlik in Turkey and Peshawar in Pakistan.

The Government's position on Area 51 ::
The U.S. Government does not explicitly acknowledge the existence of the Groom Lake facility, nor does it deny it. Unlike much of the Nellis range, the area surrounding the lake is permanently off-limits both to civilian and normal military air traffic. The area is protected by radar stations, buried movement sensors, and uninvited guests are met by helicopters and armed guards. Should they accidentally stray into the exclusionary "box" surrounding Groom's airspace, even military pilots training in the NAFR are reportedly grilled extensively by military intelligence agents.
The base does not appear on public US government maps; the USGS topological map for the area only shows the long-disused Groom Mine, and the civil aviation chart for Nevada shows a large restricted area, but defines it as part of the Nellis restricted airspace. Similarly the National Atlas page showing federal lands in Nevada doesn't distinguish between the Groom block and other parts of the Nellis range. Although officially declassified, the original film taken by US Corona spy satellite in the 1960s have been altered prior to declassification; in answer to freedom of information queries, the government responds that these exposures (which map to Groom and the entire NAFR) appear to have been destroyed (Corona image). Terra satellite images (which were publicly available) were removed from webservers (including Microsoft's "Terraserver") in 2004 ( Terraserver image), and from the monochrome 1m resolution USGS datadump made publically available. NASA Landsat 7 images are still available (these are used in the NASA World Wind program and are displayed by Google Maps). In Non-US images, including high-resolution photographs from Russian satellites and the commercial IKONOS system are also easily available (and abound on the Internet).
In response to environmental and employee lawsuits (including a class-action lawsuit brought by employees of the base for toxic waste exposure), a Presidential Determination is issued annually, exempting the Air Force's Operating Location Near Groom Lake, Nevada from environmental disclosure laws (2002 determination, 2003 determination). This (albeit tacitly) constitutes the only formal recognition the US Government has ever given that Groom Lake is more than simply another part of the Nellis complex.Nevada's state government, recognising the folklore surrounding the base might afford the otherwise neglected area some tourism potential, officially renamed the section of Nevada Highway 375 near Rachel "The Extraterrestrial Highway", and posted fancifully-illustrated signs along its length.Interlopers discovered on (or, some say, near) the restricted area are generally detained by armed private security guards (reportedly employees of defence contractor EG&G) and are then handed over to the Lincoln County sheriff.
Modest fines (of around $600) seem to be the norm, although some visitors and journalists report receiving follow-up visits from FBI agents.Although federal property within the base is exempt from state and local taxes, facilities owned by private contractors are not. One researcher has reported that the base only declares a taxable value of $2 million to the Lincoln County tax assessor, who is unable to enter the area to perform an assessment. Some Lincoln County residents have complained that the base is an unfair burden on the county, providing few local jobs (as most employees appear to live in or near Las Vegas) an iniquitous burden of land-sequestration and law-enforcement costs.