Last year, I picked up several rolls of Navy Microfilm full of engine goodies, two boxes of which were marked as “Alco 16-251A Experimental Submarine Engine”. I pulled them out when I got them, but did not go very far, as it is literally every blueprint sheet to build this engine. Thinking it was just another 251, I put them back in the box.

Last night I dove into them a bit deeper, and naturally the LAST frames on the reels (It looked like a roll of film exploded in the living room) had an elevation drawing. Cool! I devised a way to scan these, although frame by frame on my flatbed. It is a project, but it works. I need to draw up and 3D print some holders to do it more efficiently.

Click the following for larger versions.

After studying the drawing for a second, I noticed the exhaust was not connected to the intake side at all. Wait, 251’s are 4 stroke, and have a turbo…where is the turbo? There is none! That’s a roots blower on the front!

Front mounted on the engine is a blower. The discharge from the blower feeds into a raw water cooled aftercooler before going into the intake side of the engine block.

So, naturally, this raises plenty of questions. I can not find a lick of information about this engine in my usual places, so if anyone has anymore clues as to its history, shoot me a message. I don’t know if this was meant as an emergency generator engine, or propulsion. If anyone wants to build one… I have 600+ plans!