[mrlonglong]

They're unique. Originally designed to power fast torpedo boats during WW2, three of these powerful and compact engines would churn out plenty of power for the boat up to 50 kt.

https://everythingaboutboats.org/napier-deltic/

[mrlonglong]

They're still in use by our UK navy. Nine minesweepers still on active duty.

[mrlonglong]

I just realised they re-engined them with cat engines in 2008. Pity.