With the great heat wave which caused the icecaps to melt and flood the world the facilities for crafting and repairing submarines were lost to time. Those few submarines which still function are rare and the knowledge of exactly how they work is lost. Those of the technological bent have been studying them to try to figure out how to repair and replicate them. The components of the submarines have baffled a great many with their little tiny transistors and capacitors.
Now what is this dohickey? *BZZZT* Ow, that was shocking. How could something that small hold so much electricity? Right they had more tech before the world went to hell with global warming. I am starting to think that the tech caused global warming. Maybe I should go join those who use magic. Nah I couldn't live without my tinkerings. Well back to diagraming this circuit board. I know the answers are here somewhere...
The majority of submarines were used during the great wars of the 20th century, and became a major instruments of war for the militaries of the world powers.
After the great wars, submarines were seen as a tool for deep sea research. This helped in discovering several species that could live in high pressure no light environments
They started out as simple devices but as the years went on they became more and more complex.
The discovery of the submarine is a contentios subject due the theories and drawings from the 16th century. Though the creation of a fully functional submarine wasn't until the 1620's and was propelled by oars. It wasn't until the late 19th and early 20th centuries when the submarine became a tool for war. There were many different designs of submarine created. The most useful were those that could plumb the depths of the Mariana Trench and the Challenger Deep.