News has emerged of a secret US military programme intended to let troops navigate about inside huge underground enemy tunnel complexes by measuring energy pulses given off by lightning bolts.

The project is known as "Sferics-Based Underground Geolocation", or S-BUG, and is focused on building "a mapping and navigation system that provides Global Positioning System (GPS) equivalent accuracy in underground environments".

GPS signals from US military satellites are used in millions of smartphones, car sat navs and other gadgets worldwide, but they don't work without clear line-of-sight to the satellites - in other words without an unobstructed view of the sky.

Meanwhile, it seems, other US satellites - the vast fleet of sky spies operated by the American intelligence and military communities - have driven more and more people and things of interest to disappear underground. Unfortunately for the US spooks, tunnelling and subterranean engineering in general have become much cheaper in recent times, making this easier to do.

Not only does a deep tunnel complex shield an organisation from the prying orbital eyes, it is also good protection against a sudden bombing raid of the sort which destroyed Iraq's Osirak reactor in 1981 or smashed a possible nuclear facility of some kind in Syria during 2006.

Thus the world's superweapon projects, secret bases, command and control HQs etc have tended to move underground more and more: and thus the US military/spook/special-ops community has tended to ponder subterranean operations more and more.

Naturally, when wondering how to navigate deep below the Earth's surface in a hollowed-out lair where a secret superweapon is being fashioned for the purpose of holding the world to ransom, there's only one federal agency to call: DARPA, the maverick Pentagon gadgeteers who among other things created the most successful vehicle for the distribution of pornography the world has ever known*.

DARPA boffins have noted that one of the few kinds of wireless signal which can penetrate underground is low-frequency radio. Unfortunately such signals are quite hard to generate at the required power levels. A network of lo-freq RF nav stations widespread enough to offer decent accuracy would probably be impossible to deploy.

But the right kind of signals are generated naturally by lightning strikes, which cause the emission of "atmospheric" ("sferic" or "spheric") radio pulses. An underground receiver could perhaps be built capable of detecting sferics from lightning bolts hitting the surface hundreds of miles away. It could be informed of the positions of the strikes over LF comms by a single specialised surface base station, similarly far off, and thus calculate its own position from sferic data coming in from several directions.

Hence S-BUG, which was reportedly the subject of a small DARPA feasibility investigation last year. Evidently this indicated that S-BUG might just possibly be feasible, as the agency is now to hold a conference (mostly classified SECRET) for tech firms interested in taking the project forward.

Doubtless it's merely a coincidence that DARPA has lately started up another project, NIMBUS, aimed at triggering artificial lightning. ®

*The internet.