Deep-sea submarines may seem impenetrable, but in 1967, a peculiar incident enlightened scientists to just how unusual things can get while below the surface.

This particular submersible was the US Navy’s Alvin. Built in 1965, by its retirement, it had survived expeditions to the Titanic, searching for sunken hydrogen bombs, and exploring hydrothermal vents for the first time, but it received a nastly blow along the way from an unlikely predator. According to Gizmodo:

It was after the overhaul, in 1967, when Alvin got attacked by a swordfish at a depth of around 2,000 feet, during dive number 202—somewhere around the Blake Plateau and Cape Charles, in the Bahamas. The pilots heard a big metallic noise, the whole submarine shook, and something penetrated the hull. 
It was a dangerous situation, so the crew decided to get quickly back to the surface. When its mothership—105-foot catamaran Lulu—lifted Alvin off the surface, they discovered this huge swordfish stuck in the hull.

While this may seem nearly impossible, its necessary to factor in that these species of fish are so extremely aggressive that they will attack just about everything, even including sharks multiple time their size. This one just managed to both pick out a submarine and pierce it at just the right angle. Bravo!  What rewards did it get for its valiant efforts? Well, it was reportedly cooked and eaten by the crew of its intended prey.

We can only hope James Cameron avoids any encounters like these today!