By Rob Cameron
BBC News, Prague
The US and Russia are one step closer to nuclear disarmament, after signing the New Start treaty at a lavish ceremony in Prague. But a curious hangover from the threat of nuclear Armageddon is still in use across the Czech Republic.
The US and Russia signed up to cut deployed strategic warheads on Thursday
It is a feature of life in the Czech Republic which is at first unnerving, then annoying, and finally... reassuring.
Every first Wednesday of the month, at precisely midday, air raid sirens ring out across the country.
For around 140 seconds, normal conversation becomes difficult - sometimes impossible - especially if you're standing directly underneath one of the ubiquitous grey loudspeakers mounted at strategic intervals in every street, in every town and city in the country.
After the two-minute mark, the insistent high-pitched wail of the sirens begins to falter and fall, before a rather cheerful voice appears over the loudspeakers with the announcement "end of test", "end of test", and life resumes as normal.
Times of peril
The air raid sirens are not the only reminder of how close we once came to blowing each other to kingdom come
At first I thought the sirens were nothing more than a curious hangover from the Cold War, and the ever-present threat of nuclear Armageddon - rather like the British government's Protect and Survive leaflets I once discovered buried under the gas bills in my parents' kitchen drawer.
But the sirens are an integral part of the Czech Republic's present-day civil defence system, and are still used to warn the populace in times of peril.
In the 17 years I have been here, I can remember them being cranked up in anger just once, in 2002, when the floodwaters of the swollen River Vltava swept over the city's embankments and into people's homes.
That fateful August morning, I was among the hundreds of thousands of people who received an unexpected 4am wake-up call, accompanied by the ominous words "this is not a test".
This week, for the first time in many years, there was no first Wednesday of the month test - apparently it clashed with the feverish preparations for the treaty's summit the following day.
But the air raid sirens are not the only reminder of how close we once came to blowing each other to kingdom come.
Casual visitors to Prague's Metro system will notice huge sets of steel doors in the passenger tunnels. Those doors can still be hermetically sealed at a few minutes notice, creating a grim subterranean world for 400,000 souls to cower from the nuclear holocaust unfolding overhead.
A network of 800 interlinked bunkers have enough water, power and tinned food to keep the populace alive for 72 hours, before they would, presumably, be forced to emerge blinking into the radioactive daylight.
There is plenty of small print but most agree it is the necessary start... if Obama's vision of a nuclear-free world is ever to become anything more than words
The legacy of a potential nuclear cataclysm was even more evident during a trip to a Czech military installation an hour's drive southwest of Prague.
The Czech Army still uses the area for artillery practice, taking turns with local villagers who pick mushrooms in the woods.
It was here, in a nondescript field, that President Barack Obama's predecessor George W Bush wanted to build a radar base as part of the US missile defence shield.
That plan has now been abandoned, although the new administration wants to build a more flexible system in Romania and Bulgaria.
An affable defence ministry guide showed us around what used to be a Soviet missile storage facility - the gloomy underground chambers empty of their deadly cargo ever since the newly-democratic Czechoslovakia sent their former Warsaw Pact allies packing in the early 1990s.
No one - not even our guide - could say with certainty whether those missiles had carried nuclear warheads, although everyone assumes they did.
"We kept asking the Russians," he said. "But they never told us. I heard they didn't even tell our own Communist government. Anyway, the cast iron chambers no longer have any military use. They have, however, been used to store potatoes."
Change of heart
Mr Obama set out his vision for nuclear disarmament in Prague in 2009
Not far away, in the nearby village of Trokavec, the local mayor Jan Neoral is still celebrating President Obama's abandonment of the Bush missile defence plan, which also envisaged interceptor missiles in neighbouring Poland.
In response to the scheme, Russia had threatened to target its nuclear missiles at the radar base, obliterating Jan Neoral's sleepy village in a flash.
"Now Washington had changed its mind," he told me, "the military threat from Moscow has gone."
The rethink on missile defence also removed the political stumbling block to signing the New Start treaty.
Hawks and doves in Washington and Moscow are still deeply divided over what the treaty means.
Certainly, there is plenty of small print, but most agree it is the necessary start - literally and figuratively - if Mr Obama's vision of a nuclear-free world is ever to become anything more than words.
Prague's sirens and its thick metal doors in the metro are now merely a reminder of what might have been, and thankfully, was not.
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