The idea of using the Walter drive in U-boats goes back to before 1933. Actual experimental work apparently started in late 1934. The first experimental U-boat, the type V 80 (80 tons displacement) was launched in 1940. Several full sized boats followed including U-792 and U-794. One of the later large boat designs, the type XVIII, led directly to the type XXI electoboat when it became apparent that the Walter drive would not be combat ready for some time.

The Walter drive never made it as a submarine propulsion system for three reasons. No one ever got it to work reliably, certainly not during WWII. H2O2 at the high concentrations under discussion (80 - 85%) is a very unstable compound which is difficult and dangerous to handle, especially in large quantities. Reliably storing something like 200 tons of it on a submarine under combat conditions would have been extremely dangerous. There was also the issue of availability in the required quantities. Finally, the peroxide itself plus all the machinery was usable for something like 8 hours at top speed. Once the H2O2 was gone, the Walter drive became just so much ballast. It should have been apparent by 1942 that this project was a waste of resources and would not lead to a usable result in time to affect the war, however, it offered some useful spinoffs, the hull design for the electroboat and a feasible torpedo drive.

BTW, the CO2 which was produced as the only gaseous combustion product was compressed and sent overboard where it dissolved in sea water before it could rise to the surface.

Work on the Walter torpedoes began in 1938. The first model called Klippfisch, used a piston engine and ran 6500 meters at 40 knots. It reached combat status in 1942, but was never produced because a turbine driven mode, the Steinbutt, promised better performance - 8,000 meters at 45 knots. There were many problems with the turbine drive and a whole collection of versions followed all with similar performance. There were also a few long range models which used sea water injection. The best one - Steinwal - could run for 21,000 meters at 45 knots leaving no visible wake. These torpedoes turned out to be unreliable at long range since the mechanism picked up too much salt from condensed sea water. For comparison, the standard high speed torpedo (T I) was steam powered, used compressed air, ran out of fuel after 6,000 meters at 44 knots and left a clearly visible trail of nitrogen bubbles.

Apparently no Walter torpedo reached combat. In retrospect, it is clear that the Walter drive is more applicable to torpedoes than to U-boats and therefore the work on torpedoes should have been stated much earlier and with higher priority. In any event, the handling and storage problems were known at the time and it would have been a lot more realistic to concentrate on a device which uses a few hundred liters of H2O2 instead of a few hundred tons.

A type XXI armed with wire guided Steinbutt would have made a rather interesting weapon considering the type XXI sonar was accurate to ½ degree. There was a wire guided torpedo project called Spinne which carried 5,000 meters of wire. Such a torpedo could be guided into a 20 meter wide zone at a range of 2,000 meters without showing a periscope.

Regards,
SuperKraut