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Nuclear Testing at Pokhran

India conducted its first nuclear detonation, described by India as a "peaceful nuclear explosion," on 18 May 1974. This test, which may have only been partially successful, demonstrated a claimed yield of perhaps 12 kt. The underground test produced a crater with a radius variously reported at between 47 and 75 meters, and a depth of about 10 meters. The test was conducted in the Rajasthan Desert near the town of Pokhran. As is so often the case, there are several variations in the transliteration of this place name, and over time "Pokhran" has evidently replaced "Pokharan" as the preferred usage [search engine queries produce about four times as many returns for "Pokhran" as for "Pokharan", and both variants are much more common than "Pokaran"]. Althought this word surely has some meaning, this meaning is not reported in the readily available literature.

Media reports of nuclear test preparations in 1981 and 1982 located the alleged activity within the vicinity of India's first nuclear test. In April 1981, US Senator Alan Cranston, citing classified US intelligence, asserted that in in February 1981 India had begun nuclear test preparations at Pokhran. The activity was described as "surface excavations for burial of a nuclear warhead - for an underground test." Subsequently, Indian news media reported that January or February 1981 a barbed wire fence had been strung enclosing an area some eight kilometers long and three kilometers wide, about three kilometers south of the 1974 nuclear test site. Local villagers used the area around the site for grazing cattle. Further Indian media reports a year later reaffirmed these assertions. Credible evidence from several sources indicated that shafts were constructed in the early 1980s for two underground nuclear tests.

In December 1995 American intelligence satellites detected additional scientific and technical activity at the Pokaran test site in the Rajasthan desert. But intelligence experts could not tell whether the activity involved preparations for exploding a nuclear bomb or testing a ballistic missile. The site had been routinely maintained, but US intelligence noted new efforts to clean out a deep underground shaft for lowering a nuclear weapon into the earth, as well as possible preparations for instrumentation of a test to determine whether it occurred as predicted. Indian news reportes suggested the activity was associated with preparations for tests of the Prithvi missile, although no such tests subsequently occured. In January 1996 the United States presented New Delhi with a demarche demanding the test be halted. When India denied such preparations, US Ambassador Frank Wisner confronted the Indian government with satellite imagery of activity at the Pokhran site, and India's nuclear test preparations were halted.

One of the few concrete steps taken by BJP leader Atal Behari Vajpayee during his brief 13-day term as Prime Minister in May 1996 was approval for DRDO and DAE to begin preparations for a nuclear test. Reportedly, these test preparations were detected by US intelligence, provoking another demarche from the US government. However, the BJP Government fell two days before the tests could begin, and the succeeding United Front government of H.D. Deve Gowda declined to proceed.

On 11 May 1998 India carried out three underground nuclear tests at the Pokhran range. Two days later, after carrying out two more underground sub-kiloton tests, the Government announced the completion of the planned series of tests. The three underground nuclear tests carried out on 11 May were reportedly of three different devices - a fission device with a yield of about 12 KT, a thermonuclear device with a yield of about 43 KT and a sub-kiloton device. All the 3 devices were detonated simultaneously. The two tests carried out at 1221 hours on 13 May were also detonated simultaneously. The yields of the sub-kiloton devices were claimed to be in the range of 0.2 to 0.6 KT."

The Pokhran range, where India conducted its first nuclear test in 1974, is divided into four parts. Range A is used for artillery firing, with a maximum open area of 40 km. Range B is used for armor exercises, and Range C is used by the Indian Air Force. Range D, where the 1974 nuclear explosion was conducted, is a cordoned restricted area. During the 1990s normal activity at Range D reportedly consisted of few security guards and an Army engineer platoon.

The exact location of India's first test in 1974 remained obscure until a pathbreaking 1996 analysis by Vipin Gupta and Frank Pabian . This landmark study made use of satellite imagery from diverse sources, with the highest resolution being a Russian KVR-1000 scene from 24 May 1992, with a ground sample distance of between 3 and 4 meters. Through elegant analysis, Pabian and Gupta established that the 1974 test was conducted at 27.095 ± .001 degrees N, 71.752 ± .001 degrees E, some 24.8 km northwest of Pokhran town, and 12.5 km north-northwest (azimuth angle: 339 degrees) of the ISC seismic location estimate. This analysis established the existence of a bias in the seismic data, as well as the rough direction and maginitude of this bias, that produces an offset between the actual location of the test and the location indicated by seismic data alone.

The analysis of Pabian and Gupta also established that between March 1995 and March 1996, substantial activity took place at the Khetolai military range located to the immediate southwest of the 1974 nuclear explosion site. Their analysis considered evidence that pointed either to nuclear test preparations, or to Prithvi field testing, or to both possibilities.

Pabian and Gupta identified at least four sites in the central Khetolai range area that could be interpreted as associated with preparations for underground nuclear tests.

• Site A and Site C - The sites are surrounded by multiple layers of perimeter barriers, and have a rectangular structures which intersects the inferred cable lines at the center of the fenced perimeter. This fits the profile of a underground nuclear test shaft location, and the configuration resembles the layout that was used for vertical shaft tests at the US Nevada Test Site.
• Site B - This site is equidistant from both of the inferred shaft locations at Site A and Site C, which makes it suitable for serving as a diagnostics station for two nuclear tests.
• Site D - This site is located near the entrance to the central area. It can be interpreted as a support base for nuclear test preparations with an unpaved road link to the inferred control point.

The Indian government has released no information to dispell an assumption that the 1998 tests were conducted at the Khetolai military range studied by Pabian and Gupta. The open literature has affirmed this conclusion, which has remained largely unexamined, though unconfirmed.

At a 17 May 1998 Press Conference by Dr. R. Chidambaram, Chairman, AEC & Secretary, DAE, and Dr. A. P. J. Abdul Kalam, Secretary, Department of Defence Research and Development, it was stated that the nearest village [Khetolai] was a little over 5 km. away from the test site, and that the design yield of the hydrogen bomb was determined based on the location of this village. It was also stated that two devices, the thermonuclear and fission device, were detonated one kilometer apart. The detonation was simultaneous to ensure that the detonation of one did not cause damage to the other, since the shock wave has a time travel in milliseconds. When a reporter noted that there was speculation that the same site as was prepared for the 1995 tests was used in 1998, Chidambaram replied "At that time I said I do not respond to reactions of irresponsible reports in the media. I stand by this." It should be noted that the weapon design and yield details claimed at this briefing have been the subject of subsequent dispute, and there is no particular reason to accept at face value other claims made at this briefing. On some point the briefers were clearly economical with the truth, and some of their claims may have been intentionally misleading even if not entirely false.

The Indian assertion that the tests were conducted about 5 kilometers from Khetolai is completely consistent with the location of the Khetolai military range. And the assertion that the two higher-yield tests conducted on 11 May were detonated about one kilometer apart is consisetent with the separation between the suspected nuclear test areas designated Site A and Site C by Gupta and Pabian.

The Prototype International Data Center [PIDC] and the US Geological Survey both produced estimates for the location of the 11 May 1998 test. The areas of uncertainty was considerably smaller than the seismic estimates for the location of the 1974 test, though the two estimates for the 1998 tests used different data input sources, and gave almost completely divergent locations for the test. The PIDC estimate was within 3 km of the location of the Khetolai military range identified in 1996 by Pabian and Gupta, while the USGS estimate was a dozen kilometers to the northeast. Analysts concluded that Khetolai complex was used in the 11 May tests, providing a calibration for the seismic locations [Wallace - 1998].