That would be the manhole cover that got launched by Operation Plumbbob.

wasn’t there a story somewhere of a manhole cover that like broke the sound barrier or something after it got flung off by a nuclear explosion

Soviet scientists in 1957: we’re only 3 months away from launching our meticulously designed and carefully researched satellite into space! It’s going to be the first man-made object to reach space!

Operation Plumbbob: hold my manhole cover

anything can be a UFO if you throw it fast enough