sca4 | 4 years ago | on: In 2009, Two Nuclear Submarines Collided Under the Sea (2016)
Lot of dismissive reactions to these questions, but there actually are non sound related signals we use to detect submarines and there is absolutely research on how to do that from space.
This article is great, but just read the "Signal Processing" section if you're interested in space.
https://www.aspistrategist.org.au/prospects-for-game-changer...