The eyes of the world were turned spaceward in October 1957 because the Soviet Union had just launched Sputnik, the first manmade object sent into space. Or was it? Just a few weeks before, that high honor may have been achieved by something as incongruous as a manhole cover.

While aeronautical engineers were focused on space, nuclear physicists were more interested in things on the ground. More to the point, they were interested in things underground. More than a decade into the nuclear age, scientists were beginning to have serious reservations about the long-term wisdom of testing nuclear bombs out in the open.

The scientists at the Los Alamos National Laboratory in New Mexico developed plans to take parts of Operation Plumbbob (a series of 29 nuclear tests between May and October 1957) underground. This ambitious plan would allow for underground testing of nukes, thus sparing the atmosphere from further radiation contamination.

In July 1957, engineers drilled a borehole 500 feet (152 meters) deep for what was to become the world’s first underground nuclear test. Dubbed “Pascal-A”, a “small” nuclear device was detonated at the bottom of the hole. It ended up having a yield of about 50,000 greater than expected. Rather than keep radioactive fallout out of the atmosphere, it sent an impressive plume of toxic contaminants hundreds of feet in the air. One of the physicists dubbed it “the world’s finest Roman candle.”

Bureaucrats hit on the brilliant idea of putting a manhole cover over the borehole for the next test. Dr. Robert Brownlee was the scientist charged with the responsibility of capping the hole. Before doing so, he calculated the likely outcome and warned his superiors that the results would be less than ideal. Not to be deterred, the order was reaffirmed.

In preparation for Pascal-B, a bomb was placed at the bottom of a 400-foot (122-meter) hole. A two-ton concrete plug was placed on top of the bomb. At the very top, a four-inch (10-centimeter)-thick concrete and metal cap weighing at least half a ton capped off the chasm. Just for good measure, the lid was welded shut to completely seal the explosion chamber.

When the bomb went off, Dr. Brownlee’s doubts were confirmed. The concrete instantly vaporized and created a massive pressure wave within the sealed tube. The cap was woefully inadequate to contain the blast and went flying upward at a very high rate of speed.

Just how fast did it go? A high-speed camera recording the test recorded one frame per millisecond. The lid showed up in the first frame, never to be seen again. Based upon the yield and the pressure, Dr. Brownlee estimated that it left the ground at more than 37 miles (60 kilometers) per second. That comes out to 134,300 mph (216,135 kph), or more than five times the escape velocity of the planet.

To put this speed in context, the NASA X-43 A has been designated by Guinness World Records as the fastest aircraft ever made. It has a top speed of 7,000 mph (11,265 kph). The Apollo 10 capsule, on its return to earth, hit the speed of 24,791 mph (39,897 kph), thus earning a Guinness certification as the highest speed achieved by a manned vehicle. Even at that blazing speed, the capsule only reached 18% of the velocity of the Pascal-B manhole cover.

Since the manhole cover was never seen again, there is ample speculation as to whether it made it into space. It certainly was going fast enough, and if it did, it beat Sputnik into space by more than a month.

Dr. Brownlee said, “I have no idea what happened to the cap, but I always assumed that it was probably vaporized before it went into space. It is conceivable that it made it.” He added that years after the event, “When I was in Baikonur, the subject of Russia being the first to launch something into space came up. I did not raise my hand to add to the discussion, though I thought about doing so.”

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Read more fun facts about nuclear weapons.