Pakistan has been known by Western intelligence agencies to be working on more powerful "boosted fission" bombs, the type the US built in the mid-'50s. Each of those would have a yield of roughly 20 times the Hiroshima bomb. In 1986, according to a Defence Intelligence Agency report obtained by The Washington Post, Pakistan "cold-tested" its first nuclear weapon at the site, meaning it tested all the key components without actually detonating the bomb. Among the components tested was thehigh-explosive trigger for the bomb.

Here is part of what the DIA reported in 1986: Pakistan detonated a high explosive test device between September 18 and 21, 1986 as part of its continuing effort to build an implosion-type (Hiroshima-like) nuclear weapon. Later that year, Pakistan's President Zia ul-Haq and its nuclear weapons development chief A Q Khan were quoted in the Pakistani press as saying: "It is our right to obtain the technology, and when we acquire it, the Islamic world will possess it with us." It was that statement that gave rise to the fear of an "Islamic bomb."

In May 1990, during a crisis in which US intelligence believed Pakistan had weaponised its atomic bombs, spy satellites spotted ominous indicators that Pakistan could be preparing for war with India.

At Chagai, imagery analysts believed that they had spotted the nuclear weapons storage bunkers for the first time. A review of other data increased their confidence in this conclusion. A source inside Pakistan, for example, hadrevealed that A Q Khan had recently visited Chagai.

Furthermore, another reconnaissance satellite -- probably one of the newer radar-imaging satellites that could peer through the night -- had picked up a convoy of trucks that moved exactly the way their US counterparts did when they delivered nuclear weapons to US bases. Sure enough, the convoy was headed to a nearby air base.

Finally at the base was the smoking gun: F-16s were on full runway alert, with pilots sitting in their cockpits ready to light their engines and ordnance hanging from their wings. Nor was the US the only space-faring nation to peer into Pakistan that same night. Kosmos 2077, a Soviet spy satellite, followed the same path as the US not long afterwards, presumably finding the same situation.