-150 METER UNCUT FOOTAGE OF UNDERWATER ATOMIC BLAST 1958

One notable underwater atomic blast that occurred in 1958 was part of the United States' Operation Hardtack series of nuclear tests. The specific test I believe you are referring to is known as "Hardtack Umbrella," conducted on June 8, 1958, at Bikini Atoll in the Pacific Ocean.

During the Hardtack Umbrella test, a nuclear bomb, with a yield of approximately 8 kilotons, was detonated underwater. The purpose of this test was to study the effects of the explosion on various objects and structures submerged in the water, as well as to evaluate the potential impact of an underwater nuclear blast on naval vessels.

The detonation created a massive underwater shockwave, followed by a plume of water vapor and radioactive steam rising into the air. The blast caused a column of water to surge upward, forming a characteristic mushroom cloud, although the cloud formation was less prominent compared to atmospheric nuclear tests.

The effects of the underwater blast were observed and documented by military and scientific personnel, who monitored the radiation levels, the behavior of the shockwave, and the physical damage caused to nearby objects and test structures. These tests provided valuable data for understanding the potential consequences of nuclear detonations in aquatic environments.

It's important to note that I can only provide a general description based on historical information available up until September 2021. For more detailed information or specific accounts of the event, I recommend referring to reliable sources, archival footage, or historical records related to Operation Hardtack or the specific underwater nuclear tests conducted in 1958.