I'm gonna speculate on those engines a bit.
IIRC, Napier is/was a European engine manufacurer. The boats were mahogany hulled and built in Norway, according to an Internet posting I found. It's likely the Pentagon spec'd the boats in terms of on-the-water performance and survivability, with maintainability as a distant third. It's likely they required a non-magnetic hull due to concerns over mines. They almost certainly had fuel requirements that said no gasoline. Being on a gasoline powered boat with someone shooting incendiary/explosive ordinance at you is not at the top of anyone's want-to-do list.
All of this meant getting high performance using some sort of a diesel power plant. Diesels are comparatively slow turning engines, due in part to starting and stopping those heavy pistons at each end of a relatively long stroke. It looks like some engine designer had the bright idea of using two opposing short stroke pistons, instead of one long stroke piston and a cylinder head in order to form the combustion chamber. That would let the engine turn higher RPMs, which would have allowed the designers to crank out additional power.
These beasts reportedly put out 3200 HP, so it seems to have worked.
Although the engine is called a Deltec, probably because of its delta shape, it appears to actually be a V design--albeit a very unusual V.
Again, all speculation on my part. Feel free to pick it apart. /forums/images/graemlins/smile.gif
