A lesson from the long history of the Goodyear blimps is the realization that airships are exceedingly difficult to fly. That fact was well demonstrated 92 years ago, when the blimp Columbia crashed, spectacularly, in the middle of New York City.
The first class of nuclear submarines were a learning experience for the Soviet Navy. The November class boats experienced numerous difficulties and accidents, culminating in what has been described as a potential “Underwater Chernobyl."