Military submarines are fascinating examples of what can be built when most financial, environmental, and ethical constraints are removed. The article mentioned

Military submarines are fascinating examples of what can be built when most financial, environmental, and ethical constraints are removed. The article mentioned liquid metal cooled reactors. These designs allowed for very small, very fast nuclear submarines. Soviet Alfas[1] could go over 50mph, faster than many torpedoes. The craziest sub I've stumbled upon is probably the 1950's-era Seawolf[2]. Instead of lead-bismuth, its original coolant was liquid sodium. Sodium, a metal that burns on contact with water, was used as the coolant for a submerged nuclear reactor! Of course, that wasn't the only "interesting" aspect of the Seawolf's design: > The phrase "Blue Haze" was often associated with the boat, which was Cherenkov radiation, visible on a dark night, in the sea water surrounding the hull... Shake-out problems and a desire to standardize reactors caused the navy to switch away from the design, but it's still amazing that it was built and tested. https://en.wikipedia.org/wiki/Alfa-class_submarine https://en.wikipedia.org/wiki/Alfa-class_submarine https://en.wikipedia.org/wiki/USS_Seawolf_(SSN-575) https://en.wikipedia.org/wiki/USS_Seawolf_(SSN-575)