Even as The Hindu continues to break news on U.S. government surveillance of Indian public and private institutions, a host of nations that Washington considers “rogue states” appeared to showcase the best method to avoid being the target of such spying: underground facilities.

Accessing archived government documents, the National Security Archive, an anti-secrecy group, has revealed a decades-long effort by the U.S. to detect, monitor, and in some cases plan the destruction of, “more than 10,000 such facilities worldwide, many of them in hostile territory, and many presumably intended to hide or protect lethal military equipment and activities, including weapons of mass destruction, that could threaten U.S. or allied interests.”

The documents hint at frustration on the part of the Defence Intelligence Agency (DIA), the unit leading the effort, as it came up against the formidable challenge of mapping out “hardened and buried targets,” including some in Libya that were sprawling “leadership protection” complexes located 40 feet or more beneath ground level.

A 1999 DIA threat assessment stated that “The proliferation of underground facilities (UGFs) in recent years has emerged as one of the most difficult challenges facing the U.S. Intelligence Community and is projected to become even more of a problem over the next two decades.”

Citing known bunker facilities in nations such as China, Russia, Syria, Iran and North Korea — all firmly beyond the network of nations that the U.S. describes as “allies” — 21 documents unsealed this week in response to Freedom of Information Act requests suggest that UGFs were used for a range of purposes, from concealment and transportation to fuel and food storage and preservation of command and communications capabilities.

Most worrying for the DIA, however, were UGF factories for weapons productionIn 1966 Beijing was said to have launched Project 816 for an underground plutonium production reactor and a reprocessing facility near the village of Baotao in the Fuling District of Chongqing Province.

The archive documents also indicate that the U.S. had considered a number of “neutralising concepts” for the UGF’s, including to “undermine with suitcase nukes,” and “entombment” by overburdening the physical structures.

Yet there appeared to be technical challenges and in 2012 the Pentagon reportedly concluded that even its 13,600-kg Massive Ordnance Penetrator “was not capable of destroying some of Iran’s hardened underground facilities.”

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