Modern submarines can stay submerged for months at a time.
Most of us who have had a basic science class know that we breathe in oxygen and exhale carbon dioxide, or CO 2 . It's up to the flowers and trees to convert the CO 2 back into oxygen through the process of photosynthesis. I asked Robert Lemons, former Machinist's Mate Second Class on the U.S.S Henry M. Jackson, for the lowdown on this perplexing question. You know, salt, dirt, fish, poop, all the stuff that floats in the ocean. Then the water is run through a special piece of equipment called an oxygen generator.