The K-222 had an interesting design feature that made it possibly the world’s fastest submarine. The K-222’s top speed was just over 51 miles, or about 82 kilometers, per hour—making the K-222 possibly the fastest submarine ever, and plenty fast to catch surface ships. There was a drawback though: the K-222 was really loud. Though the K-222 was powered by two nuclear reactors, which are typically a quiet propulsion design, the sub’s propeller caused a great deal of cavitation—a phenomenon in which small bubbles form along the edge of a propeller and cause noise.