A few days ago I was on some TDI message board and they were discussing diesels in airplanes, the possibilities of 1.9 TDI's in airplanes and just airplane engines in general. What struck me is, that the engines are much older. Which made sense to me, because you need a very very tried-and-true type design, so as not to fall out of the sky.
Now fast-forward to today, I start reading about sub-marines. Which isn't abnormal, because I am fascinated with them. But then I catch a little paragraph on wikipedia about the Virginia class of submarines. About the diesel engines in submarines. Turns out, that before the Virginia class, they came from pre-WWII, originating in the Tambor class of submarine. That just takes tried-and-true to a whole new level! (It was a Fairbanks-Morse 38D81/8 opposed piston engine).
Finally for the Virginia class they switched to a Caterpillar 3512B V-12, which in its lowest tuned form consumes 52 gallons per hour! http://marine.cat.com/cat-3512B
I found this a very interesting contrast to automotive engines. It is a polar opposite, while car manufacturers take to new engine tech like yogi-bear to honey, other industries are far more concerned with proven technologies. In the case of submarines sticking with the same diesel engine for ~50 years!