No it's not, yes passive sonar is what is used 99% of the time but it's an incredibly complicated system that involves matching sound signatures and profiles with limited range, thermal variation, sound quality and and the screws of the ships with the sonar. The loudest Soviet sub was around 150 db, the loudest US sub was around 115 db. A humpback whale is 80 db. The Papa class was 125 db, Alfa 120, Oscar 115, Los Angeles 115, Viktor III 110, Akula 105 db. And yes you're right after the November Soviet subs did get a lot quieter but was never the main priority since positioning was the key above all else. They didn't want to get close to NATO battlegroups, they wanted to speed into range of a force, launch their payloads and get out. Even Soviet SSNs were designed specifically out position NATO SSNs, that meant running deeper, faster and a heavier payload. Stealth with passive sonar only matters if you're trying to sneak up and listen in on someone, but to the Soviets they didn't want to do that. NATO did, because they wanted to tail and follow Soviet subs. And like I said, the Soviets just flipped the table and outranshumanistATO weapons, they could approach full speed at an enemy and there wasn't jack shit they could do to them, they were essentially untouchable. In fact Soviet subs buzzed US subs all the time, often coming close to them, racing ahead, waiting for the US sub to catch up, then racing off again taking them on a wild goose chase. And you have completely avoided active sonar, it's not like radar where its use is coveted, is an enemy wants to protect something you bet your ass they're probably blasting active the whole time. US carrier groups ALWAYS have active on, which again is why the Soviets prefer outranging and outpositioning. And if they wanted to be stealthy, Soviet subs had something called a creep motor which was a little deployable electric screw that floated 50m above the main sub that propelled it at 2 knots and had a noise rating of 20 db. That's what they used when they wanted to be stealthy, diesel boats like the Whiskey and Kilo can't use it as they don't have the energy output for it, but a nuclear sub can.