They have had submarines around for more than 2 years.
There are personal submarines, nuclear submarines & the type of submarine they use in aquatic tours, & even during WWI & Civil War.
The earliest submarine was first built in 1620. It dove under the River Thames. The Confederate Navy used a submarine during the Civil War. Working as an Heating & Air Conditioning professional in the Navy, I maintained more than 2 of the submarines they now have, although I never knew when they started putting Heating & Air Conditioning idea in them. I was sure there was no AC in 1620, or they would have had it much earlier in homes. I also knew they would not have had Heating & Air Conditioning in the 1730, or 1700s, however they do now. Without Heating & Air Conditioning the guys who lived in these submarines would not have been safe. They would spend weeks under the water, & without Heating & Air Conditioning for ventilation, heating & A/C, the air would become sick, & more than 2 people would have died. I was pressing in keeping these people safe while in the submarine & under the ocean for such long times. I became an Heating & Air Conditioning professional while in the Navy, & I appreciated my task, although I couldn’t wait to finally because a normal citizen. I told my dad when I was ready to come home, & asked him if he had a position for myself and others in his Heating & Air Conditioning supplier. It was strenuous going from being a Naval officer on a submarine to being a proper civilian, although I was still doing what I appreciated. I was an Heating & Air Conditioning professional.