Anyone knows these engines?

[neurodoc]

Hello,

a friend of mine sent me images of two diesel engines which are installed on a boat, and would like to get any available information.
There is no more information on them than what you can see: like "British" on the cylinder head, and a fainted "patented" word below
Also the Word "Nation.... or National" at the base of the blocks.

Any hints?

Best regards!

[migizi]

national diesel engine
looks like a 2DM but with 4 cylinders?

does that make it a 4DM?

https://www.nationalhistoricships.or...r/2003/swallow