A few seconds after midday, a cry went up from the crowd at the Desert Inn.
It continued for several moments, a mixture of excitement and admiration which as it hung in the air seemed to mimic the very thing that had caused it. Some 65 miles to the north-west, the mushroom cloud billowed up, puffed out its chest and rolled with that boiling grey-white fervour of the radioactive explosion.
Back on the balcony, the onlookers murmured once more and sipped their cocktails suitably impressed at the rise of the USAs Atomic Age.
A mushroom cloud impresses onlookers (Photo: Las Vegas News Bureau)
It seems a remarkable and unlikely image now but 60 years ago, this was the scene that played out in hotels around Las Vegas.
On February 18 1955, at 11:59:59am, local time, the US government launched Operation Teapot, the latest of its experimental nuclear programmes on the sands of the closely guarded Nevada Test Site.
Wasp, the device at the heart of the show, was a tubby item, 1.5 metres in diameter, 3.25 metres long a Mark 6 atom bomb that bore similarities to (while being an upgrade on) the Mark 3 Fat Man which had been dropped onto the Japanese city of Nagasaki ten years earlier. Its mushroom cloud was visible for 100 miles and the states biggest city watched in awe.
Such was the naivety of the era. A generation of Americans, flushed in the afterglow of victory over Germany and Japan in 1945, but wary of the increasingly chill context of the Cold War and the iciness of relations with the Soviet Union, were suddenly in thrall to their nations status as one of the planets nuclear powers. And Uncle Sam was happy to demonstrate his new muscle, pulling deadly shapes for a pleased and patriotic audience.
Nowhere was this more the case than in Las Vegas, where explosions became cultural phenomena and reasons for parties. Hotels like the Desert Inn and Binions Horseshoe, which faced north towards the test site, were among the most enthusiastic embracers of the idea assisted by the citys Chamber of Commerce, which printed calendars with upcoming detonation times.
Above-ground explosions were held at the Nevada Test Site from 1951 to 1963 (Photo: Reuters)
Between January 1951, when the Nevada Test Site was established, and October 1963 when, in the shocked retreat from the Cuban Missile Crisis, the Limited Test Ban Treaty prohibited nuclear tests above ground the city was a regular and willing witness to the dark events that played out on and above its doorstep.
Las Vegass acceptance of the shadow of Armageddon went as far as glamour pageantry.
The atomic age was celebrated with pageantry (Photo: Las Vegas News Bureau)
Four searches were held in 1952, 1953, 1955 and 1957 for Miss Atomic, a beauty queen who could represent these ground-breaking hours. Most famously, Lee Merlin was crowned Miss Atomic Bomb in 1957.
Miss Atomic: Lee Merlin in 1957
Photos capture her smiling winningly, clutching a fluffy cotton version of a mushroom cloud to her body in lieu of a dress a dust-bowl Marilyn Monroe, all blonde hair, red lipstick and big-eyed American dreaming.
All of this played out against a backdrop of problems stored up for the future. Operation Teapot was not the first (or last) of the USAs atomic test programmes Operation Upshot-Knothole had penetrated the skies above Nevada in 1953; Operation Castle had caused immeasurable damage to the pristine archipelago of Bikini Atoll in the Marshall Islands of the South Pacific in 1954 but it was one of the most detailed.
When Wasp bellowed its hello, armoured troops were in action beneath it, toying with tactics for success on the Cold War nuclear battlefield with men coming as close to the hypocenter as 900 metres. The fallout from these explosions, meanwhile, was prone to drifting eastward on the wind where St George in southwestern Utah stood in harms way. Cases of cancer and leukemia leapt in this small city in the Fifties, Sixties and Seventies.
The effect of a blast on a house in the Yucca Flat area of the Nevada Test Site (Photo: Getty)
Skip forward over half a century, and this eager attitude to humanitys most suicidal invention is made all the more unpalatable by the blackened milestones on the road ahead.
This summer marks the 70th anniversaries of the atomic strikes which eviscerated Japan Hiroshima on August 6 1945, Nagasaki three days later on August 9 1945. Whatever your attitude to the Second World Wars endgame twin necessary evils which brought an attritional conflict to a brutal but early conclusion, and saved lives in the process; two acts of unjustifiable sledgehammer aggression against (largely) civilian targets there is nothing in these red-letter dates which merits celebration. The combined death toll from the attacks remains difficult to calculate exactly, but probably equates to a figure of somewhere between 130,000 and a quarter of a million people from the initial blasts and their radioactive aftermaths. Nobody will raise a glass or a cheer later this year.
US military officials observe the Nevada Test Site
Atomic-bomb tourism remains a possibility, of course but the process in 2015 will be one of reflection. Both Hiroshima (visithiroshima.net) and Nagasaki (visit-nagasaki.com) will host considered commemorations of their most desperate minutes while the bomb sites in both cities (see below) are compelling monuments whenever you choose to visit.
Reporters witness an explosion (Photo: Las Vegas News Bureau)
Las Vegas (lasvegas.com), meanwhile, is an ever-intriguing prospect. And while it is hard to imagine this introspective metropolis of sparkle and stardust ever again being gripped by events taking place on the horizon, it is still possible to glimpse the nuclear epoch. The National Atomic Testing Museum (see below) peers at the spectre of the bomb and its presence so close to suburbia. And Binions Horseshoe still exists too, at 128 East Fremont Street (001 702 382 1600; binions.com) though it is a faded relic these days, a casino only. Its 366 hotel rooms fell victim to the recession in 2009 and are yet to reopen.
The Desert Inn, however, is no more demolished to make space for the mega-resort Wynn Las Vegas. The final parts of the structure were imploded in November 2004. With grim irony, this detonation can be viewed online (see below).
Five key nuclear tourism sites
National Atomic Testing Museum (USA)
This fascinating institution in Las Vegas looks at the era of above-ground explosions at the Nevada Test Site with a rather more critical eye than those Fifties bomb parties.
Past perspective: The National Atomic Testing Museum looks back in Las Vegas
Photos and videos dissect this curious time in the life of Sin City, while an innovative simulated theatre show lets you experience a nuclear blast with none of the side effects.
Details: Open daily 10am-5pm (except Sunday, 12-5pm) (755 East Flamingo Road; 001 702 794 5151; nationalatomictestingmuseum.org), admission US$22 (£14).
Where it began: An obelisk marks the site of the first nuclear explosion (Photo: Samat Jain)
Trinity Site (USA)
The spot where the first nuclear explosion occurred is largely hidden from view but is offered up to the public gaze once every year, normally on the first Saturday in April (the 2015 open day will be April 4). A simple obelisk of grey stone within the closed-off military zone of the White Sands Missile Range in New Mexico marks the location where, on July 16 1945, the United States Army conducted a test detonation as part of the Manhattan Project which spawned the bombs that would land on Japan one month later.
Details: The site will be open 8am-3.30pm on April 4, free admission (001 575 678 1134; wsmr.army.mil/PAO/Trinity). The Stallion Gate entrance sits 12 miles east of the mile-marker 139 exit of the I-25 highway, some 130 miles south of Albuquerque.
The dark knight: Enola Gay is a controversial artefact 70 years after Hiroshima (Photo: AP)
Steven F. Udvar Hazy Center (USA)
This offshoot of the Smithsonian National Air and Space Museum based at Washington DCs Dulles Airport is home to one of the worlds more divisive artefacts. Is the Enola Gay the B-29 aircraft which dropped the first nuclear bomb in anger, onto Hiroshima a crucial fragment of the struggle to end the Second World War? Or is it a reminder of the moment man unlocked the door to his own destruction? Since 2003, the plane has found a home next to celebrities like the Space Shuttle Discovery and an Air France Concorde.
Details: Open daily 10am-6.30pm (14,390 Air and Space Museum Parkway, Chantilly, Virginia; 001 703 572 4118; airandspace.si.edu/visit/udvar-hazy-center), free entry.
Tacit memorial: The Atomic Bomb Dome haunts the centre of Hiroshima (Photo: Reuters)
Hiroshima Peace Memorial Museum (Japan)
Hiroshimas prime museum is an unsurprisingly sombre document to the darkness that engulfed it. Exhibits include victims possessions such as a scorched childs tricycle. The adjacent Peace Memorial Park features the citys most recognisable structure the remnants of the Hiroshima Prefectural Industrial Promotion Hall. Better known as the Atomic Bomb Dome, this unnerving ruin has been left as a wordless reminder of 1945.
Details: Open daily 8.30am-6pm (1-2 Nakajimana-cho; 0081 82 241 4004; pcf.city.hiroshima.jp/index_e2.html), admission 50 Japanese Yen (27p).
Nagasaki's Peace Park includes a statue which points accusingly at the sky (Photo: AP)
Nagasaki Atomic Bomb Museum (Japan)
The second Japanese city to suffer an atomic explosion is often overlooked as a follow-on chapter to Hiroshimas story but tells its own tale in detailed fashion at this excellent modern museum, with its blistered glass bottles, survivor accounts and clock stopped at the moment of detonation (11:02am). Alongside, the Nagasaki National Peace Memorial Hall is an elegant tribute to the dead, all glass walls and tumbling water while the nearby Peace Park has thought-provoking statues and a column marking the hypocenter.
Details: The museum is open daily 8.30am-6.30pm (7-8 Hirano-machi; 0081 95 844 1231; city.nagasaki.lg.jp/peace/english/abm), admission JPY200 (£1.10).