The fast submarines would, I think, have been Type 26 knock-offs (would you really like to serve on an HTP sub? I wouldn't), and the only extent to which they came to pass was nuclear subs. The Whiskeys were largely interpreted as Type XXI clones, but they were a lot slower (and shorter-legged); I'd guess that Zulus and Foxtrots came closest. What was largely missed in the West was a Soviet switch away from Battle of the Atlantic II to a focus on nuclear weapons (and going after Western SSBNs). It can be argued that had NATO not been crushed early on in a land war, the Soviets might have turned some of their subs loose against reinforcement shipping. We can't know, and knowing their war plans would not help, because this is speculation about what would have happened had their war plans gone sour.
As for a switch, my reading of William Taubman's magisterial and widely praised
Khrushchev: The Man and His Era (WW Norton, 2003) convinces me that the Soviet leader's emphasis on increasingly oversized H-bombs and rockets at the expense of tanks, bombers, and warships was for bluff and bluster against the apprehensive free world, rather than for imminent use. And for the Brezhnev era, to use too-brief Socratic logic: if in the maximum-danger period after Soviet total superiority in nuclear, chemical, and conventional weapons and American defeat in Vietnam but before the Reagan buildup really got going and the Chernobyl meltdown proved Soviet anti-radiation gear to be junk, had the Soviets believed they had a good chance to successfully conquer all Europe, then they would have tried to conquer all Europe. A world war was not started; therefore the Soviets never did have such assurance. They certainly did not spare lives out of any fellow feeling. Good riddance. And Desert Storm in 1991 (which Norman Friedman covered well in his book
Desert Victory: The War for Kuwait) against Iraq's superior numbers of troops and Soviet tanks using Soviet tactics convinced the USSR in its final months that its own forces were no match for the United States and Britain, and perhaps never had been, or so I have heard. Regarding Battle of the Atlantic 2 (actually 3), the fictional yet informed works
The Third World War: August 1985 and
The Third World War: The Untold Story by General Sir John Hackett (the latter clearly with input from Viktor Suvorov) and
Red Storm Rising by Tom Clancy disagree with you. But all this is getting well off topic. I look forward to publication of Dr Friedman's in-depth book on ASW during the Cold War; no doubt another good read. Groan: I will need to somehow find more bookshelf space this year, again.
P.S. I have been a longtime enthusiast for hydrogen peroxide use in aerospace planes and launch vehicles, but no, I would not want to be in a submerged submarine with that volatile substance either in the engine room or the torpedoes, despite the apparent success of the Swedes with the latter. In fact, remembering my cramped discomfort inside German and American museum subs, I would not want to be in a submerged submarine at all.
