How a Single Swedish Submarine Defeated the US Navy

Had never heard of this engine before,amazing how clever inventors
were all those years ago.

muckyman wrote:

Had never heard of this engine before,amazing how clever inventors
were all those years ago.

New for me also.  

Some time ago I actually thought about this kind of engine being a possibility.
Had no idea it was already build and being used.

Always found it a bit of a waste to have an explosion just to move the piston up and down.
Messing with fuel and then the exhaust, there are other ways of making it move.
I myself was thinking more about using electromagnetism to move the piston.
This gascompression solution is quite inventive, but tricky to build and maintain.
Perhaps this way is more energy efficient instead of using electromagnetism?