The USS Pennsylvania is an Ohio-class submarine that is powered by a nuclear reactor. The submarine must spend lots of time underwater but the crew requires lots of oxygen. The solution to the problem was making an oxygen generator. The generator works on a system of electrolysis where water molecules are exposed to electricity and split into oxygen and hydrogen atoms. The submarine can filter saltwater to normal water, can make oxygen, and has a nuclear reactor. This means they only stop at ports to get food.
This relates to engineering because engineers identified the problem of not being able to stay submerged for a long time and then used the engineering design process to make an oxygen generator.
