Germany: Super-stealth submarine powered by hydrogen fuel cells

[NickB79]

3. It uses diesel fuel to generate the hydrogen

The onboard diesel engine runs when at the surface to charge the PEM cells, which then power the electric motor for propulsion while underwater outside of snorkel range.

In the past, this same practice has been used to charge batteries instead of fuel cells. The only real difference here is that the fuel cells give it a somewhat longer endurance underwater. Diesel-electrics have been championed for their incredible silence and stealthiness for the past 30 years, to the point a 1990's-era Chinese diesel-electric snuck up on US ships during a training exercise a few years ago: http://www.dailymail.co.uk/news/article-492804/The-uninvited-guest-Chinese-sub-pops-middle-U-S-Navy-exercise-leaving-military-chiefs-red-faced.html

The lone Chinese vessel slipped past at least a dozen other American warships which were supposed to protect the carrier from hostile aircraft or submarines.

And the rest of the costly defensive screen, which usually includes at least two U.S. submarines, was also apparently unable to detect it.