Hi Stuart.... we discussed this subject in some depth in the technical section some months ago, you might find it by searching the archives....... however, in a nutshell, 90% hydrogen peroxide was introduced into a chamber with potassium permanganate, causing the peroxide to immediately break down into water and oxygen..... this was directed into a chamber into which decalin (like diesel fuel) was injected, and a spark ignited the whole thing. The resulting steam and CO2 spun a turbine, and the condensed residue was pumped overboard.
I have a copy of an atricle published in 1946 by the US navy in which they described the operation of this engine, called the Walther Engine.
The rapid revelopment of atomic power for submarines made this propulsion system redundant after 1945, but it was a brilliant technical answer to a difficult problem.