As I said, there is no such thing as a ‘sonar evading’ sub. There’s only levels of quiet. And we are the proud owners of a pre-eminent silent service.
“(Purists will note there is a third way to achieve low observability against active pinging sonar, namely the use of anechoic — sound absorbing — coatings on the hull. But modern U.S. submarine passive sonars are able to derive the range to any high-decibel sound source instantly, obviating the need to ever go active against an inbound torpedo. The implied analogy to radar-absorbent materials on cruise missiles fails underwater.)”
However, this particular quote mirrors most of the article in that it is primarily concerned with how NOT “sonar evading” enough are most anti-sub weapons that have attempted to be sonar evading.
But my recollections, regarding the Swedes, was related to the submarine itself, concerning how extremely well they employed “sound absorbing” of ITS hull and engineering that masked, or made super quiet, its engines. It was not referring to trying to make anti-sub weapons less detectable to sonar.
I might have to use my cc on Lexis-Nexis, because there is too much stuff in my old brain to remember the source.