The Walter boats and the outcome of the war
No Walter boats ever saw enemy action and no such boats even entered frontal service as only 3 boats that were intended for combat were launched before the war was ended and none of them (U-1405 - U-1407) had been taken through trials and training. Thus the Walter boats did not have any real effect on the war but they were a very interesting development and according to admiral Dönitz with a little courage and vision they could have been in service 2 years earlier and then they certainly would have had enormous impact on the war.
The fate of the Walter boats
All 10 Walter boats (3 not in commission) and the V-80 prototype (which was never commissioned into the Kriegsmarine officially) were scuttled in May 1945.
http://www.uboat.net/types/walter_hist.htm
Now the Type XX1.....
It's been a number of years (20+, actually), but I distinctly recall the sources I found stating that several of the Walther boats actually put to sea on a war patrol, but none came close to combat before the war ended and they were recalled. Regardless, the were an amazingly innovative design. As Dönitz stated, had Germany pushed development, they could have been operational several years earlier, and would have drastically altered the balance of power in the Battle of the North Atlantic. As it was, they spawned post-war development in Great Britain (and Russia, too, as I recall), which produced two Walther boats, HMS Explorer and HMS Excalibur. Both were plagued by accidents, especially fires, to due to the volatile nature of 80% Hyd-Perox. Their crews dubbed them HMS "Exploder" and HMS "Excruciator". Britain dropped the program and decommissioned the two boats when it became apparent that naval nuclear propulsion was viable and, ironically, safer. However, it did not mark the end of the Walther-cycle turbine. At least one country (Norway, I think) developed torpedoes powered by Walther engines. Don't know if they're still using them, but they were back in 1988-89.
