Lakewood - This month marks the 57th anniversary of an event that shocked the world, but that few people remember. The largest nuclear bomb ever was exploded on one of the Marshall Islands as a U.S. Military test. Harry Kissleman of Lakewood witnessed it from a ship miles away. It was a day he will never forget.

Kisselman, 79, recently told 9NEWS about his experience. The test, in March of 1954, was called "Operation Castle Bravo." The military and Energy Department planned to explode the hydrogen bomb on Bikini Atoll, one of the Marshall Islands.

Kisselman was 22 at the time, and was a sailor on a ship that carried scientists and supplies to the site. On the day of the test, his ship was about 100 miles away. He says what he saw was a total shock.

"The sky lit up, just an ungodly purple and pink, mostly pinkish. Real bright. And all you could do, you couldn't even talk to anybody, was just watch it," he said.

It turned out that the scientists and engineers had estimated wrong. The blast was two-and-a-half times more powerful than expected, making it the largest nuclear blast in history.

Kissleman says the film of the explosion is amazing because of how massive it was. The fireball was 4 miles wide in just 3 seconds. In 40 seconds, the mushroom cloud climbed to 5 miles high. The cloud caused a serious fallout situation downwind from ground zero. Hundreds of service members and local residents of nearby islands were exposed to high levels of radiation. But Kissleman was safe.

Kissleman says he thinks of that day often when he hears stories about Iran getting a nuclear bomb or a possible reactor meltdown in Japan. He says after watching that explosion he understands why it's so important that it never happens again.

"That damage, if that was ever dropped on any city, it's gonna wipe out everybody," Kissleman says. "That's how big it was and so it scared me. It always comes to mind, that aspect of it. What if somebody else had it?"